Biodegradable polyketal polymers and methods for their formation and use

ABSTRACT

The present invention relates to biodegradable biocompatible polyketals, methods for their preparation, and methods for treating animals by administration of biodegradable biocompatible polyketals. In one aspect, a method for forming the biodegradable biocompatible polyketals comprises combining a glycol-specific oxidizing agent with a polysaccharide to form an aldehyde intermediate, which is combined with a reducing agent to form the biodegradable biocompatible polyketal. The resultant biodegradable biocompatible polyketals can be chemically modified to incorporate additional hydrophilic moieties. A method for treating animals includes the administration of the biodegradable biocompatible polyketal in which biologically active compounds or diagnostic labels can be disposed. The present invention also relates to chiral polyketals, methods for their preparation, and methods for use in chromatographic applications, specifically in chiral separations. A method for forming the chiral polyketals comprises combining a glycol-specific oxidizing agent with a polysaccharide to form an aldehyde intermediate, which is combined with a suitable reagent to form the chiral polyketal. A method for use in chiral separations includes the incorporation of the chiral polyketals in the mobile phase during a chromatographic separation, or into chiral stationary phases such as gels. The present invention further relates to chiral polyketals as a source for chiral compounds, and methods for generating such chiral compounds.

PRIORITY CLAIM

The present application is a divisional application of U.S. patentapplication Ser. No. 10/501,565, filed Jul. 14, 2004, which claims thebenefit under 35 U.S.C. §371 of International Application No.:PCT/US03/01017 (International Publication No. WO 03/59988), filed Jan.14, 2003, which claims priority to U.S. Patent Application No.60/348,333, filed Jan. 14, 2002, the entire contents of each of theabove applications are incorporated herein by reference.

GOVERNMENT FUNDING

The present invention was made with U.S. government support under grantR21RR14221 awarded by the National Center for Research Resources of theNational Institutes of Health. Accordingly, the United States Governmenthas certain rights in this invention.

BACKGROUND OF THE INVENTION Biodegradable Polymers Biomedical Devicesand Drug Delivery Systems

Traditionally, pharmaceuticals have primarily consisted of smallmolecules that are dispensed orally (as solid pills and liquids) or asinjectables. Over the past three decades, however, sustained releaseformulations (i.e., compositions that control the rate of drug deliveryand allows delivery of the therapeutic agent at the site where it isneeded) have become increasingly common and complex. Nevertheless, manyquestions and challenges regarding the development of new treatments aswell as the mechanisms with which to administer them remain to beaddressed.

Although considerable research efforts in this area have led tosignificant advances, drug delivery methods/systems that have beendeveloped over the years and are currently used, still exhibit specificproblems that require some investigating. For example, many drugsexhibit limited or otherwise reduced potencies and therapeutic effectsbecause of they are generally subject to partial degradation before theyreach a desired target in the body. Once administered, sustained releasemedications deliver treatment continuously, e.g. for days or weeks,rather than for a short period of time (hours or minutes). Furthermore,orally administered therapeutics are generally preferable overinjectable medications, which are often more expensive and are morechallenging to administer, and thus it would be highly desirable ifinjectable medications could simply be dosed orally. However, this goalcannot be achieved until methods are developed to safely shepherd drugsthrough tissue barriers, such as epithelial or dermal barriers, orspecific areas of the body, such as the stomach, where low pH candegrade or destroy a medication, or through an area where healthy tissuemight be adversely affected.

One objective in the field of drug delivery systems, therefore, is todeliver medications intact to specifically targeted areas of the bodythrough a system that can control the rate and time of administration ofthe therapeutic agent by means of either a physiological or chemicaltrigger. Over the past decade, materials such as polymeric microspheres,polymer micelles, soluble polymers and hydrogel-type materials have beenshown to be effective in enhancing drug targeting specificity, loweringsystemic drug toxicity, improving treatment absorption rates, andproviding protection for pharmaceuticals against biochemicaldegradation, and thus have shown great potential for use in biomedicalapplications, particularly as components of drug delivery devices.

The design and engineering of biomedical polymers (e.g., polymers foruse under physiological conditions) are generally subject to specificand stringent requirements. In particular, such polymeric materials mustbe compatible with the biological milieu in which they will be used,which often means that they show certain characteristics ofhydrophilicity. They also have to demonstrate adequate biodegradability(i.e., they degrade to low molecular weight species. The polymerfragments are in turn metabolized in the body or excreted, leaving notrace).

Biodegradability is typically accomplished by synthesizing or usingpolymers that have hydrolytically unstable linkages in the backbone. Themost common chemical functional groups with this characteristic areesters, anhydrides, orthoesters, and amides. Chemical hydrolysis of thehydrolytically unstable backbone is the prevailing mechanism for thepolymer's degradation. Biodegradable polymers can be either natural orsynthetic. Synthetic polymers commonly used in medical applications andbiomedical research include polyethyleneglycol (pharmacokinetics andimmune response modifier), polyvinyl alcohol (drug carrier), andpoly(hydroxypropylmethacrylamide) (drug carrier). In addition, naturalpolymers are also used in biomedical applications. For instance,dextran, hydroxyethylstarch, albumin and partially hydrolyzed proteinsfind use in applications ranging from plasma substitute, toradiopharmaceutical to parenteral nutrition. In general, syntheticpolymers may offer greater advantages than natural materials in thatthey can be tailored to give a wider range of properties and morepredictable lot-to-lot uniformity than can materials from naturalsources. Synthetic polymers also represent a more reliable source of rawmaterials, one free from concerns of infection or immunogenicity.Methods of preparing polymeric materials are well known in the art.However, synthetic methods that successfully lead to the preparation ofpolymeric materials that exhibit adequate biodegradability,biocompatibility, hydrophilicity and minimal toxicity for biomedical useare scarce. The restricted number and variety of biopolymers currentlyavailable attest to this.

Therefore a need exists in the biomedical field for non-toxic,biodegradable, biocompatible, hydrophilic polymers, which overcome orminimize the above-referenced problems. Such polymers would find use inseveral applications, including components for biomedical preparations,pharmaceutical formulations, medical devices, implants, and thepackaging/delivery of therapeutic, diagnostic and prophylatic agents.

Chromatographic Applications:

Another important aspect pertaining to polymeric materials is that ofchiral polymers for use as chiral chromatographic phases for theseparation of stereoisomers.

The separation of mixtures of stereoisomers (enantiomers ordiastereomers) into individual optical isomers is one of the mostchallenging problems in analytical chemistry, reflecting practicalconsiderations important in many areas of science, particularly thepharmaceutical and agricultural industries.

For example, the pharmaceutically active site of many drugs is “chiral,”meaning that the active site is not identical to a mirror image of thesite. However, many pharmaceutical formulations marketed today areracemic mixtures of the desired compound and its “mirror image.” Theseparation of racemates of active compounds into their optical antipodeshas gained increasing importance in recent years, since it has beendemonstrated that the enantiomers of a chiral active compound oftendiffer significantly in their actions and side-effects. One optical form(or enantiomer) of a racemic mixture may be medicinally useful, whilethe other optical form may be inert or even harmful, as has beenreported to be the case for thalidomide.

Accordingly, chiral drugs are now extensively evaluated prior to largescale manufacturing, both to examine their efficacy, and to minimizeundesirable effects attributable to one enantiomer or to the interactionof enantiomers in a racemic mixture. The United States Food and DrugAdministration has recently issued new regulations governing themarketing of chiral drugs.

Early chiral separation methods used naturally occurring chiral speciesin otherwise standard separation protocols. For example, natural chiralpolymeric adsorbents such as cellulose, other polysaccharides, and woolwere used as early as the 1920's. Later strategies used other proteinsand naturally occurring chiral materials. These early strategies gavesome degree of success. However, the poor mechanical and chromatographicproperties of naturally occurring materials often complicated theseparations. Although naturally occurring chiral materials continue tobe used for chiral separations, efforts have increasingly turned tosynthesizing chiral materials having better mechanical andchromatographic properties.

Separating optical isomers often requires considerable time, effort, andexpense, even when state-of-the-art chiral separation techniques areused. There is a continuing and growing need for improved chiralseparation techniques, as well as new compositions and methods useful inchiral separations of enantiomeric mixtures.

Chiral Compounds Synthesis:

Many biologically active molecules are optically active (chiral), andusually the biological activity can vary greatly depending on theoptical purity of the molecule. As mentioned above, in pharmaceuticalapplications, the optical activity can have a great impact the activityof the drug, and thus on its marketability. Much research activity hasbeen focused on the development of technologies allowing access to pureenantiomers.

Typically, pure enantiomers may be obtained by one of three methods: (1)chiral synthesis, (2) achiral synthesis followed by indirect resolution,or (3) achiral synthesis followed by resolution by chromatography.

The ability to build optical activity into the molecule as it is beingsynthesized is an important asset, and significant research efforts havebeen devoted to the development of enantioselective syntheses in recentyears. Chiral synthesis requires a chiral starting point, it is complexand requires care to avoid racemization. The chiral purity must bemonitored throughout the synthesis. The advantages are apparent in thelong term due to the lack of wastage of the unwanted enantiomer and theability to scale up the reaction to production size. However,enantioselective syntheses are often difficult, time consuming, andrequire chiral reagents that are generally expensive.

Chiral compounds may also be obtained from achiral synthesis (which isgenerally faster, more accessible and significantly less costly than achiral synthesis), by subjecting the achiral material to indirectresolution methods such as crystallization, enzymatic reaction (whichselectively destroys the unwanted isomer), or diastereoisomericresolution (formation of the diastereomer followed by crystallization).The major drawback with these methods is that they all require a chiralselector with a very high degree of enantioselectivity, which impliesthat it must be very pure itself. An impure selector will result in aloss of purity and yield of the enantiomers resolved.

Alternatively, the separation of enantiomers may be achieved bychromatographic techniques, either by using chiral stationary phases(CSP) or chiral mobile phase additives (CMPA) to perform thechromatographic separation, or by forming a diastereomeric derivativesuitable for chromatographic separation. Nevertheless, these methodssuffer from the same disadvantages as the methods outlined above: theyare time consuming, require chiral reagents/stationary phase that aregenerally expensive, and the chromatography can also be difficult andmay take considerable development.

Therefore, a need exists for novel materials and methods that wouldeffectively and inexpensively allow access to useful chiral compounds.

SUMMARY OF THE INVENTION

The present invention discloses a polymeric material that isbiodegradable, biocompatible and exhibits little toxicity and/orbioadhesivity in vivo, and contains hydrophilic and/or pharmaceuticallyuseful groups. Specifically, the polymeric material is a polyketal.

In one aspect, the invention encompasses biodegradable biocompatiblepolyketals comprising repeat structural units, wherein substantially allthe structural units comprise (i) at least one ketal group wherein atleast one ketal oxygen atom is within the polymer main chain; and (ii)at least one hydrophilic group or pharmaceutically useful group. Inanother aspect of the invention, at least a subset of the repeatstructural units have the following chemical structure:

wherein each occurrence of R¹ and R² is a biocompatible group andincludes a carbon atom covalently attached to C¹; R^(x) includes acarbon atom covalently attached to C²; n is an integer; each occurrenceof R³, R⁴, R⁵ and R⁶ is a biocompatible group and is independentlyhydrogen or an organic moiety; and for each occurrence of the bracketedstructure n, at least one of R¹, R², R³, R⁴, R⁵ and R⁶ is eitherhydrophilic or pharmaceutically useful.

In yet another aspect, the biodegradable biocompatible polyketals of theinvention comprise repeat structural units having the following chemicalstructure:

wherein each occurrence of R² is a biocompatible group and includes acarbon atom covalently attached to C¹; R^(x) includes a carbon atomcovalently attached to C¹; n is an integer; each occurrence of R¹, R³and R⁴ is a biocompatible group and is independently hydrogen or anorganic moiety; and for each occurrence of the bracketed structure n, atleast one of R¹, R², R³ and R⁴ is either hydrophilic or pharmaceuticallyuseful.

In the above structures, n refers to the number of ketal moieties in themolecule, wherein n is an integer larger than 1. There is generally norequirement that all ketal moieties be connected to each other directly,or that the molecule be strictly regular and consist only of the repeatstructures depicted above. For example, the bracketed structures may notnecessarily be positioned in a head-to-tail fashion throughout thepolymeric chain. Irregularities may exist in the polymer backbone,whereby, for example, a number of monomeric units differ from thegeneral structures depicted above. In addition, where the polyketals ofthe invention are prepared from co-polymerization of at least twomonomers or from a polysaccharide comprising more than one type ofsaccharide moiety, the group of substituents (R¹-R⁶) in each structuralunit of the polymeric chain may not be identical throughout the polymerand they may vary from one structural unit to the next. For the purposeof the invention, it is to be understood that the substitutents R¹-R⁶ asused herein may be the same or different throughout the polymerstructure. In addition, the structures of the polyketals of theinvention are not limited to that depicted herein. The invention broadlyencompasses polyketals structures wherein at least one ketal oxygenbelongs to the main chain, and wherein substantially all monomeric unitscomprise at least one hydrophilic group or a pharmaceutically usefulgroup.

In a further aspect, the invention provides a method for forming abiodegradable polyketal which includes combining an effective amount ofa glycol-specific oxidizing agent with a polysaccharide containing ketalgroups within the main chain to open or laterally cleave thecarbohydrate rings and form an acyclic aldehyde-substituted polyketal.The aldehyde-substituted polyketal can then be utilized without furthermodification or can be reacted with a suitable reagent to derivatize thealdehyde moieties into other suitable groups, thus forming abiodegradable polyketal with the desired chemical functionality and/orphysicochemical properties.

In another aspect of the invention, a method for forming biodegradablepolyketals includes polymerization or copolymerization of suitablemonomers, such as substituted 1,3-dioxolanes; ketones and polyols (orsuitable derivatives thereof); divinyl-substituted ketals and polyols,etc. For example, the method can include reacting a suitable initiatorwith a compound having the chemical structure:

The reaction results in the formation of a polymer comprising thechemical structure:

wherein each occurrence of P¹ and P² includes a carbon atom covalentlyattached to C¹ and is independently an organic moiety or a protectedorganic moiety; P^(x) includes a carbon atom covalently attached to C²;n is an integer; each occurrence of P³, P⁴, P⁵ and P⁶ is independentlyhydrogen, an organic moiety or a protected organic moiety. For eachoccurrence of the bracketed structure n, at least one of P¹, P², P³, P⁴,P⁵ and P⁶ is either a protected hydrophilic group, or a pharmaceuticallyuseful group. In a preferred embodiment, P¹, P², P³, P⁴, P⁵ and P⁶ donot prevent polymerization. In one embodiment, the protected hydrophilicgroups or protected organic moieties of the polymer intermediate aredeprotected and optionally derivatized, thereby forming the polyketalcomprising the structure:

wherein each occurrence of R¹ and R² is a biocompatible group andincludes a carbon atom covalently attached to C¹; R^(x) includes acarbon atom covalently attached to C²; n is an integer; each occurrenceof R³, R⁴, R⁵ and R⁶ is a biocompatible group and is independentlyhydrogen or an organic moiety; and, for each occurrence of the bracketedstructure n, at least one of R¹, R², R³, R⁴, R⁵ and R⁶ is eitherhydrophilic or pharmaceutically useful. Alternatively, other ringopening techniques can be employed or developed, for example employingappropriate catalysts and resulting in the formation of polyketalscomprising unsaturated linkages within the main chain. The latter can befurther transformed into single bonds using appropriate reagents.

The present invention offers many advantages. For example, the reactantsemployed to form the biodegradable biocompatible polyketals are eitherreadily available or can be synthesized using methods generally known inthe art. Polysaccharides used for lateral cleavage with conversion toacyclic polyketals are available from plants or can be manufacturedusing methods known and practiced in biotechnology. Furthermore, theresultant biodegradable biocompatible polyketals can be modified toobtain products with desirable properties, such as by modification withadditional hydrophilic or hydrophobic moieties, pharmaceutically usefulgroups, biologically active molecules or diagnostic labels. Also, thebiodegradable biocompatible polyketal can be used as pharmaceuticalexcipients or components thereof.

The biodegradable biocompatible polyketals of the present invention arebuilt of essentially acyclic structures and therefore are distinct fromnaturally-occurring polysaccharides. For example, in certainembodiments, the polysaccharide ring structure is opened or laterallycleaved during the synthesis of the biodegradable biocompatiblepolyketals and is essentially absent from the polymer structure.Furthermore, without wishing to be bound by any particular theory, wepropose that the biodegradable biocompatible polyketals of the presentinvention may have a higher degree of biocompatability relative to thepolysaccharides from which they are derived since they generally do notcontain cyclic carbohydrates—which are potentially receptor recognizableor immunogenic. The presence or absence of cyclic structures can beestablished by Nuclear Magnetic Resonance (NMR) spectroscopy.

In another aspect, the invention provides methods for using thepolyketals in biomedical applications, primarily (nut not exclusively)in the fields of pharmacology, bioengineering, wound healing, anddermatology/cosmetics. In particular, medical applications for thebiocompatible biodegradable polymers of the invention include main oraccessory materials for the following: tablet coatings, plasmasubstitutes, gels, contact lenses, surgical implants, systems forcontrolled drug release, as ingredients of eyedrops, wound closureapplications (sutures, staples), orthopedic fixation devices (pins,rods, screws, tacks, ligaments), dental applications (guided tissueregeneration), cardiovascular applications (stents, grafts), intestinalapplications (anastomosis rings), implantable drug delivery devices andmatrices, bioresorbable templates for tissue engineering, and longcirculating and targeted drugs.

In one aspect, the invention provides a method for treating an animal,which method comprises administering the biodegradable biocompatiblepolyketal to the animal. Pharmaceutically useful components, such asbiologically active compounds or diagnostic labels, can be incorporatedinto a solution or a gel which includes the biodegradable biocompatiblepolyketal of the invention. Mixtures of such components can be disposedwithin the solution or gel. For example, pharmaceutical components canbe linked to the polyketal by a chemical bond or dispersed throughoutthe biocompatible biodegradable polyketal solution or gel.

In another aspect, the present invention provides chiral polyketals,methods of preparation and methods of use thereof. For example, chiralpolyketals in accordance with the invention may find use inchromatographic applications, specifically in chiral separations. Suchchiral polyketals can be incorporated in the mobile phase during achromatographic separation, or they could instead be incorporated intochiral stationary phases such as gels, wall coatings, and packed columnsand capillaries through means known in the art.

A further aspect of the invention provides methods of using the chiralpolyketals of the present invention as a valuable alternative source forchiral compounds. For instance, depolymerization (e.g., hydrolysis,enzymatic degradation or acidic treatment in organic media) of thechiral polyketals of the present invention will result in the monomericcomponents ketones and alcohols, or in hydroxyketones, which are chiralmoieties, and can thus be used for enantioselective syntheses. Certainfunctional groups of the polyketals may have to be protected beforeinitiating depolymerization, using methods known in the art in order togenerate final products with the desired functionality.

DEFINITIONS

“Biocompatible”: The term “biocompatible”, as used herein is intended todescribe compounds that exert minimal destructive or host responseeffects while in contact with body fluids or living cells or tissues.Thus a biocompatible group, as used herein, refers to an aliphatic,alicyclic, heteroaliphatic, heteroalicyclic, aryl or heteroaryl moiety,which falls within the definition of the term biocompatible, as definedabove and herein. The term “Biocompatibility” as used herein, is alsotaken to mean minimal interactions with recognition proteins, e.g.,naturally occurring antibodies, cell proteins, cells and othercomponents of biological systems. However, substances and functionalgroups specifically intended to cause the above effects, e.g., drugs andprodrugs, are considered to be biocompatible. Preferably, compounds are“biocompatible” if their addition to normal cells in vitro, atconcentrations similar to the intended in vivo concentration, results inless than or equal to 5% cell death during the time equivalent to thehalf-life of the compound in vivo (e.g., the period of time required for50% of the compound administered in vivo to be eliminated/cleared), andtheir administration in vivo induces minimal inflammation, foreign bodyreaction, immunotoxicity, chemical toxicity or other such adverseeffects. In the above sentence, the term “normal cells” refers to cellsthat are not intended to be destroyed by the compound being tested. Forexample, non-transformed cells should be used for testingbiocompatibility of antineoplastic compounds.

“Biodegradable”: As used herein, “biodegradable” polymers are polymersthat are susceptible to biological processing in vivo. As used herein,“biodegradable” compounds are those that, when taken up by cells, can bebroken down by the lysosomal or other chemical machinery or byhydrolysis into components that the cells can either reuse or dispose ofwithout significant toxic effect on the cells. The degradation fragmentspreferably induce no or little organ or cell overload or pathologicalprocesses caused by such overload or other adverse effects in vivo.Examples of biodegradation processes include enzymatic and non-enzymatichydrolysis, oxidation and reduction. Suitable conditions fornon-enzymatic hydrolysis, for example, include exposure of thebiodegradable polyketals to water at a temperature and a pH of lysosomalintracellular compartment. Biodegradation of polyketals of the presentinvention can also be enhanced extracellularly, e.g. in low pH regionsof the animal body, e.g. an inflamed area, in the close vicinity ofactivated macrophages or other cells releasing degradation facilitatingfactors. In certain preferred embodiments, the effective size of thepolymer at pH˜7.5 does not detectably change over 1 to 7 days, andremains within 50% of the original polymer size for at least severalweeks. At pH˜5, on the other hand, the polymer preferably detectablydegrades over 1 to 5 days, and is completely transformed into lowmolecular weight fragments within a two-week to several-month timeframe. Polymer integrity in such tests can be measured, for example, bysize exclusion HPLC. Although faster degradation may be in some casespreferable, in general it may be more desirable that the polymerdegrades in cells with the rate that does not exceed the rate ofmetabolization or excretion of polymer fragments by the cells. Inpreferred embodiments, the polymers and polymer biodegradationbyproducts are biocompatible.

“Hydrophilic”: The term “hydrophilic” as it relates to substituents onthe polymer monomeric units does not essentially differ from the commonmeaning of this term in the art, and denotes organic moieties whichcontain ionizable, polar, or polarizable atoms, or which otherwise maybe solvated by water molecules. Thus a hydrophilic group, as usedherein, refers to an aliphatic, alicyclic, heteroaliphatic,heteroalicyclic, aryl or heteroaryl moiety, which falls within thedefinition of the term hydrophilic, as defined above. Examples ofparticular hydrophilic organic moieties which are suitable include,without limitation, aliphatic or heteroaliphatic groups comprising achain of atoms in a range of between about one and twelve atoms,hydroxyl, hydroxyalkyl, amine, carboxyl, amide, carboxylic ester,thioester, aldehyde, nitryl, isonitryl, nitroso, hydroxylamine,mercaptoalkyl, heterocycle, carbamates, carboxylic acids and theirsalts, sulfonic acids and their salts, sulfonic acid esters, phosphoricacids and their salts, phosphate esters, polyglycol ethers, polyamines,polycarboxylates, polyesters and polythioesters. In preferredembodiments of the present invention, at least one of the polymermonomeric units include a carboxyl group (COOH), an aldehyde group(CHO), a methylol (CH₂OH) or a glycol (for example, CHOH—CH₂OH orCH—(CH₂OH)₂).

“Hydrophilic”: The term “hydrophilic” as it relates to the polymers ofthe invention generally does not differ from usage of this term in theart, and denotes polymers comprising hydrophilic functional groups asdefined above. In a preferred embodiment, hydrophilic polymer is awater-soluble polymer. Hydrophilicity of the polymer can be directlymeasured through determination of hydration energy, or determinedthrough investigation between two liquid phases, or by chromatography onsolid phases with known hydrophobicity, such as, for example, C4 or C18.

“Biomolecules”: The term “biomolecules”, as used herein, refers tomolecules (e.g., proteins, amino acids, peptides, polynucleotides,nucleotides, carbohydrates, sugars, lipids, nucleoproteins,glycoproteins, lipoproteins, steroids, etc.) which belong to classes ofchemical compounds, whether naturally-occurring or artificially created(e.g., by synthetic or recombinant methods), that are commonly found incells and tissues. Specific classes of biomolecules include, but are notlimited to, enzymes, receptors, neurotransmitters, hormones, cytokines,cell response modifiers such as growth factors and chemotactic factors,antibodies, vaccines, haptens, toxins, interferons, ribozymes,anti-sense agents, plasmids, DNA, and RNA.

“Physiological conditions”: The phrase “physiological conditions”, asused herein, relates to the range of chemical (e.g., pH, ionic strength)and biochemical (e.g., enzyme concentrations) conditions likely to beencountered in the extracellular fluids of living tissues. For mostnormal tissues, the physiological pH ranges from about 7.0 to 7.4.Circulating blood plasma and normal interstitial liquid representtypical examples of normal physiological conditions.

“Polysaccharide”, “carbohydrate” or “oligosaccharide”: The terms“polysaccharide”, “carbohydrate”, or “oligosaccharide” are known in theart and refer, generally, to substances having chemical formula(CH₂0)_(n), where generally n>2, and their derivatives. Carbohydratesare polyhydroxyaldehydes or polyhydroxyketones, or change to suchsubstances on simple chemical transformations, such as hydrolysis,oxydation or reduction. Typically, carbohydrates are present in the formof cyclic acetals or ketals (such as, glucose or fructose). Said cyclicunits (monosaccharides) may be connected to each other to form moleculeswith few (oligosaccharides) or several (polysaccharides) monosaccharideunits. Often, carbohydrates with well defined number, types andpositioning of monosaccharide units are called oligosaccharides, whereascarbohydrates consisting of mixtures of molecules of variable numbersand/or positioning of monosaccharide units are called polysaccharides.The terms “polysaccharide”, “carbohydrate”, and “oligosaccharide”, areused herein interchangeably. A polysaccharide may include natural sugars(e.g., glucose, fructose, galactose, mannose, arabinose, ribose, andxylose) and/or modified sugars (e.g., 2′-fluororibose, 2′-deoxyribose,and hexose).

“Small molecule”: As used herein, the term “small molecule” refers tomolecules, whether naturally-occurring or artificially created (e.g.,via chemical synthesis) that have a relatively low molecular weight.Preferred small molecules are biologically active in that they produce alocal or systemic effect in animals, preferably mammals, more preferablyhumans. Typically, small molecules have a molecular weight of less thanabout 1500 g/mol. In certain preferred embodiments, the small moleculeis a drug. Preferably, though not necessarily, the drug is one that hasalready been deemed safe and effective for use by the appropriategovernmental agency or body. For example, drugs for human use listed bythe FDA under 21 C.F.R. §§330.5, 331 through 361, and 440 through 460;drugs for veterinary use listed by the FDA under 21 C.F.R. §§500 through589, incorporated herein by reference, are all considered suitable foruse with the present hydrophilic polymers.

Classes of small molecule drugs that can be used in the practice of thepresent invention include, but are not limited to, vitamins, anti-AIDSsubstances, anti-cancer substances, antibiotics, immunosuppressants,anti-viral substances, enzyme inhibitors, neurotoxins, opioids,hypnotics, anti-histamines, lubricants, tranquilizers, anti-convulsants,muscle relaxants and anti-Parkinson substances, anti-spasmodics andmuscle contractants including channel blockers, miotics andanti-cholinergics, anti-glaucoma compounds, anti-parasite and/oranti-protozoal compounds, modulators of cell-extracellular matrixinteractions including cell growth inhibitors and anti-adhesionmolecules, vasodilating agents, inhibitors of DNA, RNA or proteinsynthesis, anti-hypertensives, analgesics, anti-pyretics, steroidal andnon-steroidal anti-inflammatory agents, anti-angiogenic factors,anti-secretory factors, anticoagulants and/or antithrombotic agents,local anesthetics, ophthalmics, prostaglandins, anti-depressants,anti-psychotic substances, anti-emetics, imaging agents. Many largemolecules are also drugs.

A more complete, although not exhaustive, listing of classes andspecific drugs suitable for use in the present invention may be found in“Pharmaceutical Substances: Syntheses, Patents, Applications” by AxelKleemann and Jurgen Engel, Thieme Medical Publishing, 1999 and the“Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals”,Edited by Susan Budavari et al., CRC Press, 1996, both of which areincorporated herein by reference.

“Pharmaceutically useful group or entity”: As used herein, the termPharmaceutically useful group or entity refers to a compound or fragmentthereof, or an organic moiety which, when associated with the polyketalpolymers of the present invention, can exert some biological ordiagnostic function or activity when administered to a subject, orenhance the therapeutic, diagnostic or preventive properties of thepolyketal in biomedical applications, or improve safety, alterbiodegradation or excretion, or is detectable. Examples of suitablepharmaceutically useful groups or entities includehydrophilicity/hydrophobicity modifiers, pharmacokinetic modifiers,biologically active modifiers, detectable modifiers. A modifier can haveone or more pharmaceutical functions, e.g., biological activity andpharmacokinetics modification. Pharmacokinetics modifiers can include,for example, antibodies, antigens, receptor ligands, hydrophilic,hydrophobic or charged groups. Biologically active modifiers include,for example, therapeutic drugs and prodrugs, antigens, immunomodulators.Detectable modifiers include diagnostic labels, such as radioactive,fluorescent, paramagnetic, superparamagnetic, ferromagnetic, X-raymodulating, X-ray-opaque, ultrasound-reflective, and other substancesdetectable by one of available clinical or laboratory methods, e.g.,scintigraphy, NMR spectroscopy, MRI, X-ray tomography, sonotomography,photoimaging, radioimmunoassay. Modifiers can be small molecules ormacromolecules, and can belong to any chemical or pharmaceutical class,e.g., nucleotides, chemotherapeutic agents, antibacterial agents,antiviral agents, immunomodulators, hormones or analogs thereof,enzymes, inhibitors, alkaloids and therapeutic radionuclides. Viral andnon-viral gene vectors are considered to be a pharmaceutically usefulentity or group. For the purpose of this invention, the group ofchemotherapeutic agents include, but is not limited to, topoisomerase Iand II inhibitors, alkylating agents, anthracyclines, doxorubicin,cisplastin, carboplatin, vincristine, mitromycine, taxol, camptothecin,antisense oligonucleotides, ribozymes, and dactinomycines.

“Macromolecule”: As used herein, the term macromolecule refers tomolecules, whether naturally-occurring or artificially created (e.g.,via chemical synthesis) that have a relatively high molecular weight,generally above 1500 g/mole Preferred macromolecules are biologicallyactive in that they exert a biological function in animals, preferablymammals, more preferably humans. Examples of macromolecules includeproteins, enzymes, growth factors, cytokines, peptides, polypeptides,polylysine, proteins, lipids, polyelectrolytes, immunoglobulins, DNA,RNA, ribozymes, plasmids, and lectins. For the purpose of thisinvention, supramolecular constructs such as viruses and proteinassociates (e.g., dimers) are considered to be macromolecules. Whenassociated with the polyketals of the invention, a macromolecule may bechemically modified prior to being associated with said biodegradablebiocompatible polyketal.

“Diagnostic label”: As used herein, the term diagnostic label refers toan atom, group of atoms, moiety or functional group, a nanocrystal, orother discrete element of a composition of matter, that can be detectedin vivo or ex vivo using analytical methods known in the art. Whenassociated with a biodegradable biocompatible polyketal of the presentinvention, such diagnostic labels permit the monitoring of thebiodegradable biocompatible polyketal in vivo. On the other hand,constructs and compositions that include diagnostic labels can be usedto monitor biological functions or structures. Examples of diagnosticlabels include, without limitations, labels that can be used in medicaldiagnostic procedures, such as, radiopharmaceutical or radioactiveisotopes for gamma scintigraphy and Positron Emission Tomography (PET),contrast agent for Magnetic Resonance Imaging (MRI) (for exampleparamagnetic atoms and superparamagnetic nanocrystals), contrast agentfor computed tomography, contrast agent for X-ray imaging method, agentfor ultrasound diagnostic method, agent for neutron activation, andmoiety which can reflect, scatter or affect X-rays, ultrasounds,radiowaves and microwaves, fluorophores in various optical procedures,etc.

“Effective amount of a glycol-specific oxidizing agent”: as it relatesto the oxidative cleavage of the polysaccharides referred to in thepresent invention, the phrase effective amount of a glycol-specificoxidizing agent means an amount of the glycol-specific oxidizing agentthat provides oxidative opening of essentially all carbohydrate rings ofa polysaccharide.

“Aliphatic”: In general, the term aliphatic, as used herein, includesboth saturated and unsaturated, straight chain (i.e., unbranched) orbranched aliphatic hydrocarbons, which are optionally substituted withone or more functional groups, as defined below. As will be appreciatedby one of ordinary skill in the art, “aliphatic” is intended herein toinclude, but is not limited to, alkyl, alkenyl, alkynyl moieties. Thus,as used herein, the term “alkyl” includes straight and branched alkylgroups. An analogous convention applies to other generic terms such as“alkenyl”, “alkynyl” and the like. Furthermore, as used herein, theterms “alkyl”, “alkenyl”, “alkynyl” and the like encompass bothsubstituted and unsubstituted groups. In certain embodiments, as usedherein, “lower alkyl” is used to indicate those alkyl groups(substituted, unsubstituted, branched or unbranched) having 1-6 carbonatoms. In certain embodiments, the alkyl, alkenyl and alkynyl groupsemployed in the invention contain 1-20 aliphatic carbon atoms. Incertain other embodiments, the alkyl, alkenyl, and alkynyl groupsemployed in the invention contain 1-10 aliphatic carbon atoms. In yetother embodiments, the alkyl, alkenyl, and alkynyl groups employed inthe invention contain 1-8 aliphatic carbon atoms. In still otherembodiments, the alkyl, alkenyl, and alkynyl groups employed in theinvention contain 1-6 aliphatic carbon atoms. In yet other embodiments,the alkyl, alkenyl, and alkynyl groups employed in the invention contain1-4 carbon atoms.

Illustrative aliphatic groups thus include, but are not limited to, forexample, methyl, ethyl, n-propyl, isopropyl, allyl, n-butyl, sec-butyl,isobutyl, tert-butyl, n-pentyl, sec-pentyl, isopentyl, tert-pentyl,n-hexyl, sec-hexyl, moieties and the like, which again, may bear one ormore substituents, as previously defined. Alkenyl groups include, butare not limited to, for example, ethenyl, propenyl, butenyl,1-methyl-2-buten-1-yl, and the like. Representative alkynyl groupsinclude, but are not limited to, ethynyl, 2-propynyl (propargyl),1-propynyl and the like.

“Alicyclic”: The term alicyclic, as used herein, refers to compoundswhich combine the properties of aliphatic and cyclic compounds andinclude but are not limited to cyclic, or polycyclic aliphatichydrocarbons and bridged cycloalkyl compounds, which are optionallysubstituted with one or more functional groups, as defined below. Aswill be appreciated by one of ordinary skill in the art, “alicyclic” isintended herein to include, but is not limited to, cycloalkyl,cycloalkenyl, and cycloalkynyl moieties, which are optionallysubstituted with one or more functional groups. Illustrative alicyclicgroups thus include, but are not limited to, for example, cyclopropyl,—CH₂-cyclopropyl, cyclobutyl, —CH₂-cyclobutyl, cyclopentyl,—CH₂-cyclopentyl-n, cyclohexyl, —CH₂-cyclohexyl, cyclohexenylethyl,cyclohexanylethyl, norborbyl moieties and the like, which again, maybear one or more substituents.

“Heteroaliphatic”: The term “heteroaliphatic”, as used herein, refers toaliphatic moieties in which one or more carbon atoms in the main chainhave been substituted with an heteroatom. Thus, a heteroaliphatic grouprefers to an aliphatic chain which contains one or more oxygen sulfur,nitrogen, phosphorus or silicon atoms, e.g., in place of carbon atoms.Heteroaliphatic moieties may be saturated or unsaturated, branched orlinear (i.e., unbranched), and substituted or unsubstituted.Substituents include, but are not limited to, any of the substitutentsmentioned below, i.e., the substituents recited below resulting in theformation of a stable compound.

“Heteroalicyclic”: The term heteroalicyclic, as used herein, refers tocompounds which combine the properties of heteroaliphatic and cycliccompounds and include but are not limited to saturated and unsaturatedmono- or polycyclic heterocycles such as morpholino, pyrrolidinyl,furanyl, thiofuranyl, pyrrolyl etc., which are optionally substitutedwith one or more functional groups. Substituents include, but are notlimited to, any of the substitutents mentioned below, i.e., thesubstituents recited below resulting in the formation of a stablecompound.

“Alkyl”: the term alkyl as used herein refers to saturated, straight- orbranched-chain hydrocarbon radicals derived from a hydrocarbon moietycontaining between one and twenty carbon atoms by removal of a singlehydrogen atom, which alkyl groups are optionally substituted with one ormore functional groups. Substituents include, but are not limited to,any of the substitutents mentioned below, i.e., the substituents recitedbelow resulting in the formation of a stable compound. Examples of alkylradicals include, but are not limited to, methyl, ethyl, propyl,isopropyl, n-butyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, n-heptyl,n-octyl, n-decyl, n-undecyl, and dodecyl.

“Alkoxy”: the term alkoxy as used herein refers to an alkyl groups, aspreviously defined, attached to the parent molecular moiety through anoxygen atom. Examples include, but are not limited to, methoxy, ethoxy,propoxy, isopropoxy, n-butoxy, tert-butoxy, neopentoxy, and n-hexoxy.

“Alkenyl”: the term alkenyl denotes a monovalent group derived from ahydrocarbon moiety having at least one carbon-carbon double bond by theremoval of a single hydrogen atom, which alkenyl groups are optionallysubstituted with one or more functional groups. Substituents include,but are not limited to, any of the substitutents mentioned below, i.e.,the substituents recited below resulting in the formation of a stablecompound. Alkenyl groups include, for example, ethenyl, propenyl,butenyl, 1-methyl-2-buten-1-yl, and the like.

“Alkynyl”: the term alkynyl as used herein refers to a monovalent groupderived form a hydrocarbon having at least one carbon-carbon triple bondby the removal of a single hydrogen atom, which alkenyl groups areoptionally substituted. Substituents include, but are not limited to,any of the substitutents mentioned below, i.e., the substituents recitedbelow resulting in the formation of a stable compound. Representativealkynyl groups include ethynyl, 2-propynyl (propargyl), 1-propynyl, andthe like.

“Amine”: the term amine as used herein refers to one, two, or three,respectively, alkyl groups, as previously defined, attached to theparent molecular moiety through a nitrogen atom. The term alkylaminorefers to a group having the structure —NHR′ wherein R′ is an alkylgroup, as previously defined; and the term dialkylamino refers to agroup having the structure —NR′R″, wherein R′ and R″ are eachindependently selected from the group consisting of alkyl groups. Theterm trialkylamino refers to a group having the structure —NR′R″R′″,wherein R′, R″, and R′″ are each independently selected from the groupconsisting of alkyl groups. Additionally, R′, R″, and/or R′″ takentogether may optionally be —(CH₂)_(k)— where k is an integer from 2 to6. Example include, but are not limited to, methylamino, dimethylamino,ethylamino, diethylamino, diethylaminocarbonyl, methylethylamino,iso-propylamino, piperidino, trimethylamino, and propylamino.

“Aryl”: The term aryl, as used herein, refers to stable mono- orpolycyclic, unsaturated moieties having preferably 3-14 carbon atoms,each of which may be substituted or unsubstituted. Substituents include,but are not limited to, any of the substitutents mentioned below, i.e.,the substituents recited below resulting in the formation of a stablecompound. The term aryl may refer to a mono- or bicyclic carbocyclicring system having one or two aromatic rings including, but not limitedto, phenyl, naphthyl, tetrahydronaphthyl, indanyl, indenyl and the like.

“Heteroaryl”: The term heteroaryl, as used herein, refers to a stableheterocyclic or polyheterocyclic, unsaturated radical having from fiveto ten ring atoms of which one ring atom is selected from S, O and N;zero, one or two ring atoms are additional heteroatoms independentlyselected from S, O and N; and the remaining ring atoms are carbon, theradical being joined to the rest of the molecule via any of the ringatoms. Heteroaryl moieties may be substituted or unsubstituted.Substituents include, but are not limited to, any of the substitutentsmentioned below, i.e., the substituents recited below resulting in theformation of a stable compound. Examples of heteroaryl nuclei includepyridyl, pyrazinyl, pyrimidinyl, pyrrolyl, pyrazolyl, imidazolyl,thiazolyl, oxazolyl, isooxazolyl, thiadiazolyl, oxadiazolyl, thiophenyl,furanyl, quinolinyl, isoquinolinyl, and the like.

It will also be appreciated that aryl and heteroaryl moieties, asdefined herein may be attached via an aliphatic, alicyclic,heteroaliphatic, heteroalicyclic, alkyl or heteroalkyl moiety and thusalso include (aliphatic)aryl, -(heteroaliphatic)aryl,-(aliphatic)heteroaryl, -(heteroaliphatic)heteroaryl, -(alkyl)aryl,-(heteroalkyl)aryl, -(heteroalkyl)aryl, and -(heteroalkyl)heteroarylmoieties. Thus, as used herein, the phrases “aryl or heteroaryl” and“aryl, heteroaryl, -(aliphatic)aryl, -(heteroaliphatic)aryl,-(aliphatic)heteroaryl, -(heteroaliphatic)heteroaryl, -(alkyl)aryl,-(heteroalkyl)aryl, -(heteroalkyl)aryl, and -(heteroalkyl)heteroaryl”are interchangeable.

“Carboxylic acid”: The term carboxylic acid as used herein refers to agroup of formula —CO₂H.

“Halo, halide and halogen”: The terms halo, halide and halogen as usedherein refer to an atom selected from fluorine, chlorine, bromine, andiodine.

“Methylol”: The term methylol as used herein refers to an alcohol groupof the structure —CH₂OH.

“Hydroxyalkyl”: As used herein, the term hydroxyalkyl refers to an alkylgroup, as defined above, bearing at least one OH group.

“Mercaptoalkyl”: The term mercaptoalkyl as used therein refers to analkyl group, as defined above, bearing at least one SH group

“Heterocyclic”: The term heterocyclic, as used herein, refers to anon-aromatic partially unsaturated or fully saturated 3- to 10-memberedring system, which includes single rings of 3 to 8 atoms in size and bi-and tri-cyclic ring systems which may include aromatic six-membered arylor aromatic heterocyclic groups fused to a non-aromatic ring.Heterocyclic moieties may be substituted or unsubstituted. Substituentsinclude, but are not limited to, any of the substitutents mentionedbelow, i.e., the substituents recited below resulting in the formationof a stable compound. Heterocyclic rings include those having from oneto three heteroatoms independently selected from oxygen, sulfur, andnitrogen, in which the nitrogen and sulfur heteroatoms may optionally beoxidized and the nitrogen heteroatom may optionally be quaternized.

“Acyl”: The term acyl, as used herein, refers to a group comprising acarbonyl group of the formula C═O. Examples of acyl groups includealdehydes, ketones, carboxylic acids, acyl halides, anhydrides,thioesters, amides and carboxylic esters.

“Hydrocarbon”: The term hydrocarbon, as used herein, refers to anychemical group comprising hydrogen and carbon. The hydrocarbon may besubstituted or unsubstituted. The hydrocarbon may be unsaturated,saturated, branched, unbranched, cyclic, polycyclic, or heterocyclic.Illustrative hydrocarbons include, for example, methyl, ethyl, n-propyl,iso-propyl, cyclopropyl, allyl, vinyl, n-butyl, tert-butyl, ethynyl,cyclohexyl, methoxy, diethylamino, and the like. As would be known toone skilled in this art, all valencies must be satisfied in making anysubstitutions.

“Substituted”: The terms substituted, whether preceded by the term“optionally” or not, and substituent, as used herein, refers to thereplacement of hydrogen radicals in a given structure with the radicalof a specified substituent. When more than one position in any givenstructure may be substituted with more than one substituent selectedfrom a specified group, the substituent may be either the same ordifferent at every position. As used herein, the term “substituted” iscontemplated to include all permissible substituents of organiccompounds. In a broad aspect, the permissible substituents includeacyclic and cyclic, branched and unbranched, carbocyclic andheterocyclic, aromatic and nonaromatic substituents of organiccompounds. Heteroatoms such as nitrogen may have hydrogen substituentsand/or any permissible substituents of organic compounds describedherein which satisfy the valencies of the heteroatoms. Examples ofsubstituents include, but are not limited to aliphatic; alicyclic;heteroaliphatic; heteroalicyclic; aryl; heteroaryl; alkylaryl;alkylheteroaryl; alkoxy; aryloxy; heteroalkoxy; heteroaryloxy;alkylthio; arylthio; heteroalkylthio; heteroarylthio; F; Cl; Br; I; —OH;—NO₂; —CN; —CF₃; —CH₂CF₃; —CHCl₂; —CH₂OH; —CH₂CH₂OH; —CH₂NH₂;—CH₂SO₂CH₃; —C(O)R_(x); —CO₂(R_(x)); —CON(R_(x))₂; —OC(O)R_(x);—OCO₂R_(x); —OCON(R_(x))₂; —N(R_(x))₂; —S(O)₂R_(x); —NR_(x)(CO)R_(x)wherein each occurrence of R_(x) independently includes, but is notlimited to, aliphatic, alicyclic, heteroaliphatic, heteroalicyclic,aryl, heteroaryl, alkylaryl, or alkylheteroaryl, wherein any of thealiphatic, alicyclic, heteroaliphatic, heteroalicyclic, alkylaryl, oralkylheteroaryl substituents described above and herein may besubstituted or unsubstituted, branched or unbranched, cyclic or acyclic,and wherein any of the aryl or heteroaryl substituents described aboveand herein may be substituted or unsubstituted.

The following are more general terms used throughout the presentapplication:

“Animal”: The term animal, as used herein, refers to humans as well asnon-human animals, at any stage of development, including, for example,mammals, birds, reptiles, amphibians, fish, worms and single cells. Cellcultures and live tissue samples are considered to be pluralities ofanimals. Preferably, the non-human animal is a mammal (e.g., a rodent, amouse, a rat, a rabbit, a monkey, a dog, a cat, a primate, or a pig). Ananimal may be a transgenic animal or a human clone.

“Associated with”: When two entities are “associated with” one anotheras described herein, they are linked by a direct or indirect covalent ornon-covalent interaction. Preferably, the association is covalent.Desirable non-covalent interactions include hydrogen bonding, van derWaals interactions, hydrophobic interactions, magnetic interactions,electrostatic interactions, or combinations thereof, etc.

“Effective amount”: In general, as it refers to an active agent or drugdelivery device, the term “effective amount” refers to the amountnecessary to elicit the desired biological response. As will beappreciated by those of ordinary skill in this art, the effective amountof an agent or device may vary depending on such factors as the desiredbiological endpoint, the agent to be delivered, the composition of theencapsulating matrix, the target tissue, etc. For example, the effectiveamount of microparticles containing an antigen to be delivered toimmunize an individual is the amount that results in an immune responsesufficient to prevent infection with an organism having the administeredantigen.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 depicts the size exclusion chromatogram of the reaction mixtureobtained in Example 2, containing poly[1-hydroxymethyl-1-(2-hydroxy-1-hydroxymethyl-ethoxy)-ethylene oxide](e.g., PHMHO), the product of oxidative cleavage/reduction of inulin.Detection: refraction index. Column: BioRad BioSil SEC 125. Eluent:water, 0.9% NaCl. Apparent MW: 3 tp 7 kDa (90% of material).

FIG. 2 depicts the proton NMR spectrum of the reaction mixture obtainedin Example 2, containing poly[1-hydroxymethyl-1-(2-hydroxy-1-hydroxymethyl-ethoxy)-ethylene oxide](e.g., PHMHO), the product of oxidative cleavage/reduction of inulin.

FIG. 3 depicts the size exclusion chromatogram of the reaction mixtureobtained in Example 4, containing poly(hydroxymethylethylenedi(hydroxymethyl)ketal) (e.g., PHMK), the product of oxidativecleavage/reduction of levan. Detection: refraction index. Column: BioRadBioSil SEC 125. Eluent: water, 0.9% NaCl. Apparent MW: 3 to 200 kDa (90%of material).

FIG. 4: depicts the proton NMR spectrum of the reaction mixture obtainedin Example 4, containing poly(hydroxymethylethylenedi(hydroxymethyl)ketal) (e.g., PHMK), the product of oxidativecleavage/reduction of levan.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS OF THE INVENTION

Certain preferred embodiments of the invention will now be moreparticularly described and pointed out in the claims. It will beunderstood that the particular embodiments of the invention are shown byway of illustration and not as limitations of the invention. Theprinciple features of the invention may be employed in variousembodiments without departing from the scope of the invention.

Biodegradable Biocompatible Polyketals

Novel concepts in pharmacology and bioengineering impose new, morespecific and more stringent requirements on biomedical polymers.Ideally, advanced macromolecular materials would combine negligiblereactivity in vivo with low toxicity and biodegradability. Polymerstructure should support an ample set of technologies for polymerderivatization, for example, conjugation with drugs, cell-specificligands, or other desirable modifiers. Materials combining all the abovefeatures would be useful in the development of macromolecular drugs,drug delivery systems, implants and templates for tissue engineering.

On the chemistry level, developing such biocompatible and biodegradablematerials translates into developing macromolecules with minimizedinteractions in vivo, main chains susceptible to hydrolysis (e.g.,degradation) in vivo, and readily modifiable functional groups. Anotherconsideration to take into account is that both the main chain and thefunctional groups interact with an extremely complex biological milieu,and all interactions may be amplified via cooperative mechanisms.

Biomolecule interactions in vivo are mediated by several components ofcell surfaces, extracellular matrix, and biological fluids. For example,both biomolecule internalization by cells and cell adhesion topolymer-coated surfaces can be mediated by several cell surfaceelements, many of which are functionally specialized. Cooperativebinding, often referred to as “non-specific interactions”, is anothermajor factor of biomolecule (and surface) reactivity in vivo. Cellinteractions with polymers and recognition protein-polymer complexesalso have an element of cooperativity. The very nature of cooperativeinteractions in complex systems suggests that any large molecule cansignificantly interact with a complex substrate for the simple reasonthat, because the binding energy is additive, the association constantof cooperative binding (K_(a)) would grow with the number ofassociations exponentially. In other words, any polymer of a sufficientlength can be expected to interact with at least one of the variouscomponents of a biological system. Even if a molecule of certain sizeshows low interactions in cell cultures and in vivo, a larger moleculeof the same type (or a supra molecular assembly) can have a much higherbinding activity.

In summary, even if polymer molecules are assembled of domains that donot interact with cell receptors and recognition proteins, suchmolecules can be capable of cooperative interactions in vivo; i.e.,completely inert polymers may not exist at all. However, severalbiomolecules and biological interfaces do appear to be functionallyinert, except for their specialized signaling domains. For example,plasma proteins are known to circulate for several weeks without uptakein the reticuloendothelial system (RES), unlike artificial constructs ofcomparable size that have never been reported to have comparable bloodhalf-lives. Without wishing to be bound to any particular theory, wepropose that the mutual “inertness” of natural biomolecules and surfacesmay relate to their relatively uniform interface structures, where thepotential binding sites are always saturated by naturally occurringcounteragents present in abundance. Therefore, emulation of the commoninterface structures can result in a material that would not activelyinteract with actually existing binding sites because these sites wouldbe pre-occupied by the natural “prototypes”.

Poly- and oligosaccharides are the most abundant interface moleculesexpressed (as various glycoconjugates) on cell surfaces, plasmaproteins, and proteins of the extracellular matrix. Therefore, theinvention encompasses structural emulation of interface carbohydrates inan effort to identify and exclude all structural components that can berecognized, even with low affinity, by any biomolecule, especially bycell receptors and recognition proteins.

All interface carbohydrates have common structural domains which appearto be irrelevant to their biological function. The acetal/ketal groupand the adjacent atoms are present in all carbohydrates regardless ofbiological activity, whereas the receptor specificity of each moleculedepends on the structure and configuration of the glycol domains of thecarbohydrate rings. Thus it would seem that biologically inert(“stealth”) polymers could be obtained using substructures that form theacetal/ketal structures of the carbohydrate rings; i.e., the —O—C—O—group and adjacent carbons. Although functional groups that are commonin naturally occurring glycoconjugates (e.g., OH groups) can be used assubstitutents, the potentially biorecognizable combinations of thesegroups, such as rigid structures at C1-C2-C3-C4 (in pyranoses) is notdesirable.

The present invention is founded on the recognition that themacromolecular products of the cleavage of at least one of thecarbon-carbon bonds in the C1-C2-C3-C4 portion in substantially all thecarbohydrate rings of a polysaccharide would have the desired properties(e.g., an essentially inert biocompatible hydrophilic polymer). Inaddition, synthetic strategies designed to position the polysaccharideacetal/ketal groups within the main chain of the resultingmacromolecular product would ensure degradability via proton-catalyzedhydrolysis.

Biocompatible biodegradable polyacetals according to this concept havebeen described in U.S. Pat. Nos. 5,811,510; 5,863,990 and 5,958,398,incorporated herein by reference (Papisov M., “Biodegradable PolyacetalPolymers and Methods for their Formation and Use”). Polyacetals differfrom polyketals in that the structure of their hydrolysis sensitivegroup is —O—CHR—O— (polyacetals) rather than —O—CR¹R²—O— (polyketals).This difference results in the generally different physical shape of thepolymer molecule, different depolymerization products, and can provideproducts with different and useful sensitivity to pH, the action ofwater and other reagents. In addition, polyketals may offer variousother advantages over polyacetals. For example, polyketals generallyhave more functional groups per monomer unit, which allows a higherdegree of derivatization. In addition, without wishing to be bound byany particular theory, we propose that the increased steric hindrance ofthe ketal group caused by the additional substituent may result inpolymers with higher resistance to the components of normal biologicalmilieu. This increased steric hinderance may also translate into longermaterial lifetime in chiral separation applications. Another advantageof the present invention is that several known polyketoses found inplants, such as levans and other fructans, which currently have no use,can be transformed into useful products. Cells producing suchpolysaccharides may be selected, cloned and transformed to produce,after polysaccharide treatment, polyketals with novel and more usefulstructures and properties. Yet another advantage of the polyketals ofthe present invention resides in the different chemical structure ofterminal groups of polyketals, for example polyketals derived from1,2-ketoses. For instance, upon partial hydrolysis, the resultingfragments of such polyketals comprise a terminal ketone group, whichallows selective one-stage terminal modification. In another aspect, thepolyketals of the invention present the additional advantage thatdepolymerization of protected hydrophilic polyketals can provideinexpensive protected derivatives of substituted ketones, which may bevaluable in organic synthesis. In addition, another advantage is thatdifferent functional group geometry may provide better polycationicpolyketals for DNA packaging for non-viral gene therapy.

The present invention encompasses biodegradable biocompatiblehydrophilic polyketals, derivatives and conjugates thereof, as well asmethods of preparation and methods of use thereof.

As described in Example 1, we have successfully made biodegradablebiocompatible polyketals which are hydrophilic, hydrolyzable and can befunctionalized to include pharmaceutically useful groups. In a preferredembodiment, the polyketals of the present invention have at least one ofthe ketal oxygen atoms in each monomer unit positioned within the mainchain. This ensures that the degradation process (viahydrolysis/cleavage of the polymer ketal groups) will result infragmentation of the polyketal to the monomeric components (i.e.,degradation), and confers to the polyketals of the invention theirbiodegradable properties. The properties (e.g., solubility,bioadhesivity and hydrophilicity) of biodegradable biocompatiblepolyketals can be modified by subsequent substitution of additionalhydrophilic or hydrophobic groups. The novelty of the present inventionrelates in part to the structure and properties of hydrophilicpolyketals comprising ketal groups in the main chain.

Synthetic methods for the preparation of polymers containing ketalgroups are known in the art (see for example, “Hydrophobically modifiedpoly(acetal-polyethers)” Sau A. C., U.S. Pat. No. 5,574,127; “Method forpreparing polyacetals and polyketals by emulsion polymerization” Chou Y.J. et al., U.S. Pat. No. 4,374,953; “Positive-workingradiation-sensitive copying composition and method of using to formrelief images: Sander J. et al., U.S. Pat. No. 4,247,611). However, anumber of them contain ketal groups outside the main chain; e.g., onsubstitutents or as chemical modifiers for polyketones (see for example“Method for converting polyketals to polyaryletherketones in thepresence of a metal salt” Kelsey D. R., U.S. Pat. No. 4,882,397). Thushydrolysis of the ketal groups in such polymeric materials, unlike thepolymers of the present invention, does not result in degradation(depolymerization) of the polymer.

Polyketals known in the art generally comprise hydrophobic substituentsand thus generally have limited water solubility. In addition, themethods of making them generate relatively low molecular weight polymers(5-50 kDa). Additionally, most polyketals have hydrophobic domains and,consequently, their biocompatability is limited. Hydrophobic polymersare vulnerable to non-specific interactions with proteins and lipids,which also may cause undesirable side effects. Finally, most knownsynthetic polyketals typically have a hydrophobic main chain that doesnot degrade readily in vivo.

In summary, while a person of ordinary skill in the art has a variety ofavailable synthetic methods at their disposal to prepare polyketals,there is no motivation to select biocompatible, biodegradable,hydrophilic polyketals. Furthermore, even if there was motivation to doso, there is no reasonable expectation that it would succeed. Thepresent invention provides (i) access to biocompatible biodegradablehydrophilic polyketals, (ii) methods for their preparation and (iii)examples of applications where they might find use.

In a preferred embodiment, the polymers of the present inventioncomprise ketal groups within the main chain. Although it is notnecessary that the entire ketal group be positioned within the polymerbackbone, it is desirable that at least one of the ketal oxygen atomsbelongs to the main chain. Accordingly, one embodiment of the presentinvention provides biodegradable biocompatible polyketals comprisingrepeat structural units, wherein substantially all the structural unitscomprise (i) at least one ketal group wherein at least one ketal oxygenatom is within the polymer main chain; and (ii) at least one hydrophilicgroup or pharmaceutically useful group. In another aspect of theinvention, at least a subset of the repeat structural units have thefollowing chemical structure:

wherein each occurrence of R¹ and R² is a biocompatible group andincludes a carbon atom covalently attached to C¹; R^(x) includes acarbon atom covalently attached to C²; n is an integer; each occurrenceof R³, R⁴, R⁵ and R⁶ is a biocompatible group and is independentlyhydrogen or an organic moiety; and for each occurrence of the bracketedstructure n, at least one of R¹, R², R³, R⁴, R⁵ and R⁶ is eitherhydrophilic or pharmaceutically useful.

In yet another aspect, the biodegradable biocompatible polyketals of theinvention comprise repeat structural units having the following chemicalstructure:

wherein each occurrence of R² is a biocompatible group and includes acarbon atom covalently attached to C¹; R^(x) includes a carbon atomcovalently attached to C¹; n is an integer; each occurrence of R¹, R³and R⁴ is a biocompatible group and is independently hydrogen or anorganic moiety; and for each occurrence of the bracketed structure n, atleast one of R¹, R², R³ and R⁴ is either hydrophilic or pharmaceuticallyuseful.

Examples of suitable organic moieties are aliphatic groups having achain of atoms in a range of between about one and twelve atoms,hydroxyl, hydroxyalkyl, amine, carboxyl, amide, carboxylic ester,thioester, aldehyde, nitryl, isonitryl, nitroso, hydroxylamine,mercaptoalkyl, heterocycle, carbamates, carboxylic acids and theirsalts, sulfonic acids and their salts, sulfonic acid esters, phosphoricacids and their salts, phosphate esters, polyglycol ethers, polyamines,polycarboxylates, polyesters, polythioesters, pharmaceutically usefulgroups, a biologically active substance or a diagnostic label.

In preferred embodiments of the present invention, for each occurrenceof the bracketed structure n, at least one of R¹, R², R³, R⁴, R⁵ and R⁶includes a carboxyl group (COOH), an aldehyde group (CHO), a methylol(CH₂OH) or a glycol group. In another preferred embodiment of thepresent invention, at least one of R¹, R², R³, R⁴, R⁵ and R⁶ contains anatom or a moiety that increases the polymer hydrophilicity or allowsconjugation with other compounds.

In still another preferred embodiment of the present invention R¹, R²,R³, R⁴, R⁵ or R⁶ are methylol or glycol. In yet another preferredembodiment of the present invention, R¹ and R² comprise a methylol orglycol group and R³, R⁴, R⁵ and R⁶ are hydrogen.

In exemplary embodiments of the invention, the polyketal comprises thefollowing chemical structure:

In yet another embodiment of the present invention, at least one of R¹,R², R³, R⁴, R⁵ and R⁶ contains a chiral moiety. In exemplary embodimentsof the invention, the polyketal comprises the following chemicalstructure:

In yet another embodiment of the present invention, at least one of R¹,R², R³, R⁴, R⁵ and R⁶ is a nitrogen-containing compound. Thenitrogen-containing compound can be a pharmaceutically useful group, adrug, a macromolecule, a diagnostic label, a crosslinking agent or afunctional group which is suitable as a modifier of biodegradablebiocompatible polyketal behavior in vivo. Examples of such functionalgroups include antibodies, their fragments, receptor ligands and othercompounds that selectively interact with biological systems.

Alternatively, the nitrogen-containing compound can have a chemicalstructure of —C_(m)H_(2m)NR⁷R⁸, wherein m is an integer. In oneembodiment, n is one. R⁷ and R⁸ can include hydrogen, organic orinorganic substituents. Examples of suitable organic or inorganic groupsinclude aliphatic groups, aromatic groups, complexes of heavy metals,etc.

In one aspect of the invention, the biodegradable biocompatiblepolyketals can be crosslinked. A suitable crosslinking agent has theformula X¹—(R) —X², where R is a spacer group and X¹ and X² are reactivegroups. X¹ and X² can be different or the same. The spacer group R maybe an aliphatic, alicyclic, heteroaliphatic, heteroalicyclic, aryl orheteroaryl moiety. Examples of suitable spacer groups includebiodegradable or nonbiodegradable groups, for example, aliphatic groups,carbon chains containing biodegradable inserts such as disulfides,esters, etc. The term “reactive group,” as it relates to X¹ and X²,means functional groups which can be connected by a reaction within thebiodegradable biocompatible polyketals, thereby crosslinking thebiodegradable biocompatible polyketals. Suitable reactive groups whichform crosslinked networks with the biodegradable biocompatiblepolyketals include epoxides, halides, tosylates, mesylates,carboxylates, aziridines, cyclopropanes, esters, N-oxysuccinimideesters, disulfides, anhydrides etc.

In one of the preferred embodiments of the present invention, thebiodegradable biocompatible polyketals are crosslinked withepibromohydrin, or epichlorohydrin. More preferably, the epibromohydrinor epichlorohydrin is present in an amount in the range of between aboutone and about twenty five percent by weight of the crosslinkedbiodegradable biocompatible polyketals.

Alternatively, the term “reactive” group as it relates to X¹ and X²means a nucleophilic group that can be reacted with an aldehydeintermediate of the biodegradable biocompatible polyketals, therebycrosslinking the biodegradable biocompatible polyketals. Suitablereactive groups for the aldehyde intermediate include amines, thiols,polyols, alcohols, ketones, aldehydes, diazocompounds, boronderivatives, ylides, isonitriles, hydrazines and their derivatives andhydroxylamines and their derivatives, etc.

In one embodiment, the biodegradable biocompatible polyketals of thepresent invention have a molecular weight of between about 0.5 and about1500 kDa. In a preferred embodiment of the present invention, thebiodegradable biocompatible polyketals have a molecular weight ofbetween about 1 and about 1000 kDa.

In one embodiment, polyketals are modified at one or both of thetermini, for example:

wherein n is an integer and R′, R″ and R′″ may be hydrophilic,pharmaceutically useful, or otherwise useful for the purposes of thisinvention. For example, R′ can comprise an N-hydroxysuccinimide ester ora maleimide for conjugation with proteins; R″ and R′″ can comprise aphospholipid and a target specific moiety, such as antibody,respectively, for liposome modification.

In another embodiment, polyketals can be substituted at one terminal andone or more non-terminal positions, or at both terminal and one or morenon-terminal positions.

In one embodiment, at least one of R¹, R², R³, R⁴, R⁵ and R⁶ cancomprise a small molecule, a pharmaceutically useful group, a drug, amacromolecule or a diagnostic label. Examples of suitable drug moleculescomprise a biologically active functional group fragment or moiety.Specific examples of suitable drug molecules include vitamins, anti-AIDSsubstances, anti-cancer substances, antibiotics, immunosuppressants,anti-viral substances, enzyme inhibitors, neurotoxins, opioids,hypnotics, anti-histamines, lubricants, tranquilizers, anti-convulsants,muscle relaxants and anti-Parkinson substances, anti-spasmodics andmuscle contractants including channel blockers, miotics andanti-cholinergics, anti-glaucoma compounds, anti-parasite and/oranti-protozoal compounds, modulators of cell-extracellular matrixinteractions including cell growth inhibitors and anti-adhesionmolecules, vasodilating agents, inhibitors of DNA, RNA or proteinsynthesis, anti-hypertensives, analgesics, anti-pyretics, steroidal andnon-steroidal anti-inflammatory agents, anti-angiogenic factors,anti-secretory factors, anticoagulants and/or antithrombotic agents,local anesthetics, ophthalmics, prostaglandins, anti-depressants,anti-psychotic substances, anti-emetics, and imaging agents.

Examples of pharmaceutically useful groups include, but are not limitedto: hydrophilicity/hydrophobicity modifiers, pharmacokinetic modifiers,antigens, receptor ligands, nucleotides, chemotherapeutic agents,antibacterial agents, antiviral agents, immunomodulators, hormones andtheir analogs, enzymes, inhibitors, alkaloids, therapeuticradionuclides, etc. Suitable chemotherapeutic compounds are, forexample, topoisomerase I and II inhibitors, alkylating agents,anthracyclines, doxorubicin, cisplastin, carboplatin, vincristine,mitromycine, taxol, camptothecin, antisense oligonucleotides, ribozymes,dactinomycines, etc. Other suitable compounds include therapeuticradionuclides, such as β-emitting isotopes of rhenium, cesium, iodine,and alkaloids, etc. In one embodiment of the present invention, at leastone of R¹, R², R³, R⁴, R⁵ and R⁶ contains doxorubicin, taxol, orcamptothecin.

In another embodiment of the present invention, at least one of R¹, R²,R³, R⁴, R⁵ and R⁶ comprises a diagnostic label. Examples of suitablediagnostic labels include diagnostic radiopharmaceutical or radioactiveisotopes for gamma scintigraphy and PET, contrast agent for MagneticResonance Imaging (MRI) (for example paramagnetic atoms andsuperparamagnetic nanocrystals), contrast agent for computed tomography,contrast agent for X-ray imaging method, agent for ultrasound diagnosticmethod, agent for neutron activation, and moiety which can reflect,scatter or affect X-rays, ultrasounds, radiowaves and microwaves,fluorophores in various optical procedures, etc. Diagnosticradiopharmaceuticals include γ-emitting radionuclides, e.g., indium-111,technetium-99m and iodine-131, etc. Contrast agents for MRI (MagneticResonance Imaging) include magnetic compounds, e.g. paramagnetic ions,iron, manganese, gadolinium, lanthanides, organic paramagnetic moietiesand superparamagnetic, ferromagnetic and antiferromagnetic compounds,e.g., iron oxide colloids, ferrite colloids, etc. Contrast agents forcomputed tomography and other X-ray based imaging methods includecompounds absorbing X-rays, e.g., iodine, barium, etc. Contrast agentsfor ultrasound based methods include compounds which can absorb, reflectand scatter ultrasound waves, e.g., emulsions, crystals, gas bubbles,etc. Still other examples include substances useful for neutronactivation, such as boron and gadolinium. Further, substituents can beemployed which can reflect, refract, scatter, or otherwise affectX-rays, ultrasound, radiowaves, microwaves and other rays useful indiagnostic procedures. Fluorescent labels can be used for photoimaging.In a preferred embodiment, at least one of R¹, R² and R³ comprises aparamagnetic ion or group.

In yet another embodiment, the polyketals of the present invention areassociated with a macromolecule. Examples of suitable macromoleculesinclude, but are not limited to, enzymes, polypeptides, polylysine,proteins, lipids, polyelectrolytes, antibodies, ribonucleic anddeoxyribonucleic acids and lectins. The macromolecule may be chemicallymodified prior to being associated with said biodegradable biocompatiblepolyketal. Circular and linear DNA and RNA (e.g., plasmids) andsupramolecular associates thereof, such as viral particles, for thepurpose of this invention are considered to be macromolecules.

Polyketals according to the present invention are expected to bebiodegradable, in particular upon uptake by cells, and relatively“inert” in relation to biological systems. The products of degradationare preferably uncharged and do not significantly shift the pH of theenvironment.

In one embodiment, postsynthetic modification of the polyketals of theinvention allows the introduction of a variety of functional groups. Itis proposed that the abundance of alcohol groups may provide low rate ofpolymer recognition by cell receptors, particularly of phagocytes. Thepolymer backbones of the present invention generally contain few, ifany, antigenic determinants (characteristic, for example, forpolysaccharides and polypeptides) and generally do not comprise rigidstructures capable of engaging in “key-and-lock” type interactions.Thus, the soluble, crosslinked and solid polyketals of this inventionare predicted to have low toxicity and bioadhesivity, which makes themsuitable for several biomedical applications.

Biodegradable Biocompatible Polyketals—Methods of Preparation

According to the present invention, any available techniques can be usedto make the inventive polyketals or compositions including them. Forexample, semi-synthetic and fully synthetic methods such as thosediscussed in detail below may be used.

Certain compounds of the present invention, and definitions of specificfunctional groups are also described in more detail herein. For purposesof this invention, the chemical elements are identified in accordancewith the Periodic Table of the Elements, CAS version, Handbook ofChemistry and Physics, 75^(th) Ed., inside cover, and specificfunctional groups are generally defined as described therein.Additionally, general principles of organic chemistry, as well asspecific functional moieties and reactivity, are described in “OrganicChemistry”, Thomas Sorrell, University Science Books, Sausalito: 1999,the entire contents of which are incorporated herein by reference.Furthermore, it will be appreciated by one of ordinary skill in the artthat the synthetic methods, as described herein, utilize a variety ofprotecting groups. By the term “protecting group”, has used herein, itis meant that a particular functional moiety, e.g., O, S, or N, istemporarily blocked so that a reaction can be carried out selectively atanother reactive site in a multifunctional compound. In preferredembodiments, a protecting group reacts selectively in good yield to givea protected substrate that is stable to the projected reactions; theprotecting group must be selectively removed in good yield by readilyavailable, preferably nontoxic reagents that do not attack the otherfunctional groups; the protecting group forms an easily separablederivative (more preferably without the generation of new stereogeniccenters); and the protecting group has a minimum of additionalfunctionality to avoid further sites of reaction. As detailed herein,oxygen, sulfur, nitrogen and carbon protecting groups may be utilized.For example, in certain embodiments, certain exemplary oxygen protectinggroups may be utilized. These oxygen protecting groups include, but arenot limited to methyl ethers, substituted methyl ethers (e.g., MOM(methoxymethyl ether), MTM (methylthiomethyl ether), BOM(benzyloxymethyl ether), PMBM (p-methoxybenzyloxymethyl ether), to namea few), substituted ethyl ethers, substituted benzyl ethers, silylethers (e.g., TMS (trimethylsilyl ether), TES (triethylsilylether), TIPS(triisopropylsilyl ether), TBDMS (t-butyldimethylsilyl ether), tribenzylsilyl ether, TBDPS (t-butyldiphenyl silyl ether), to name a few), esters(e.g., formate, acetate, benzoate (Bz), trifluoroacetate,dichloroacetate, to name a few), carbonates, cyclic acetals and ketals.In certain other exemplary embodiments, nitrogen protecting groups areutilized. These nitrogen protecting groups include, but are not limitedto, carbamates (including methyl, ethyl and substituted ethyl carbamates(e.g., Troc), to name a few) amides, cyclic imide derivatives, N-Alkyland N-Aryl amines, imine derivatives, and enamine derivatives, to name afew. Certain other exemplary protecting groups are detailed herein,however, it will be appreciated that the present invention is notintended to be limited to these protecting groups; rather, a variety ofadditional equivalent protecting groups can be readily identified usingthe above criteria and utilized in the present invention. Additionally,a variety of protecting groups are described in “Protective Groups inOrganic Synthesis” Third Ed. Greene, T. W. and Wuts, P. G., Eds., JohnWiley & Sons, New York: 1999, the entire contents of which are herebyincorporated by reference.

Semi-Synthetic Route

In a preferred embodiment, the carbohydrate rings of a suitablepolysaccharide can be oxidized by glycol-specific reagents, resulting inthe cleavage of carbon-carbon bonds between carbon atoms that are eachconnected to a hydroxyl group. For example, without wishing to be boundto any particular theory, we propose that oxidative cleavage of 1->2polyfructoses (a.k.a. 2,1-polyfructoses) in accordance with the presentinvention proceeds through the following mechanism:

This process can be complicated, depending on experimental conditions,by the formation of intra and interpolymer hemiacetals which can inhibitfurther polysaccharide oxidation. Oxidative cleavage of polysaccharidesapplied to the preparation of hydrophilic polyacetals has been reported(U.S. Pat. Nos. 5,811,510; 5,863,990; 5,958,398). The preparation ofhydrophilic polyketals by this method, however, has remainedunsuccessful until recently. Previous attempts failed to produce theexpected polyketal chain, and yielded a fragmented product instead,whereby the polymeric backbone was cleaved during the reaction. Theidentification of suitable polysaccharides as starting material,together with the optimization of the reaction conditions to achievebetter control of the oxidative opening (“lateral cleavage”) of thepolysaccharide rings, resulted in the successful preparation ofhydrophilic polyketals in high yield and high molecular weights. Thus,in the present invention, it can be demonstrated that the oxidation of asuitable polysaccharide, followed by reduction, leads to the synthesisof macromolecular biodegradable biocompatible polyketals. The structureof the biodegradable biocompatible polyketal obtained by the abovementioned method is dependent upon the precursor polysaccharide.

In one embodiment, a method for forming the biodegradable biocompatiblepolyketals of the present invention comprises a process by which asuitable polysaccharide is combined with an effective amount of aglycol-specific oxidizing agent to form an aldehyde intermediate. Thealdehyde intermediate, which is a polyketal of this invention by itself,is then reacted with a suitable reagent to form a biodegradablebiocompatible polyketal comprising repeat structural units, whereinsubstantially all the structural units comprise (i) at least one ketalgroup wherein at least one ketal oxygen atom is within the polymer mainchain; and (ii) at least one hydrophilic group or pharmaceuticallyuseful group. Thus, in certain embodiments, a method for forming thebiodegradable biocompatible polyketals comprises steps of: a) reactingan effective amount of an oxidizing agent with a polysaccharide to forma biodegradable biocompatible polyketal aldehyde; b) optionally treatingthe biodegradable biocompatible polyketal aldehyde with a suitablereagent under suitable conditions to form said biodegradablebiocompatible polyketal polymer; and c) optionally repeating step b)until the desired functionalization of said biodegradable biocompatiblepolyketal is achieved; thereby forming a biodegradable biocompatiblepolyketal comprising repeat structural units, wherein substantially allthe structural units comprise: i) at least one ketal group wherein atleast one ketal oxygen atom is within the polymer main chain; and ii) atleast one hydrophilic group or pharmaceutically useful group.

In another embodiment, at least a subset of the repeat structural unitshave the following chemical structure:

wherein each occurrence of R¹ and R² is a biocompatible group andincludes a carbon atom covalently attached to C¹; R^(x) includes acarbon atom covalently attached to C²; n is an integer; each occurrenceof R³, R⁴, R⁵ and R⁶ is a biocompatible group and is independentlyhydrogen or an organic moiety; and for each occurrence of the bracketedstructure n, at least one of R¹, R², R³, R⁴, R⁵ and R⁶ is eitherhydrophilic or pharmaceutically useful.

In yet another embodiment, the biodegradable biocompatible polyketals ofthe invention comprise repeat structural units having the followingchemical structure:

wherein each occurrence of R² is a biocompatible group and includes acarbon atom covalently attached to C¹; R^(x) includes a carbon atomcovalently attached to C¹; n is an integer; each occurrence of R¹, R³and R⁴ is a biocompatible group and is independently hydrogen or anorganic moiety; and for each occurrence of the bracketed structure n, atleast one of R¹, R², R³ and R⁴ is either hydrophilic or pharmaceuticallyuseful.

Examples of suitable organic moieties include, but are not limited to,aliphatic groups having a chain of atoms in a range of between about oneand twelve atoms, hydroxyl, hydroxyalkyl, amine, carboxyl, amide,carboxylic ester, thioester, aldehyde, nitryl, isonitryl, nitroso,hydroxylamine, mercaptoalkyl, heterocycle, carbamates, carboxylic acidsand their salts, sulfonic acids and their salts, sulfonic acid esters,phosphoric acids and their salts, phosphate esters, polyglycol ethers,polyamines, polycarboxylates, polyesters, polythioesters,pharmaceutically useful groups, a biologically active substance or adiagnostic label.

The biodegradable biocompatible polyketals of the invention can beprepared to meet desired requirements of biodegradability andhydrophilicity. For example, under physiological conditions, a balancebetween biodegradability and stability can be reached. For instance, itis known that macromolecules with molecular weights beyond a certainthreshold (generally, above 50-100 kDa, depending on the physical shapeof the molecule) are not excreted through kidneys, as small moleculesare, and can be cleared from the body only through uptake by cells anddegradation in intracellular compartments, most notably lysosomes. Thisobservation exemplifies how functionally stable yet biodegradablematerials may be designed by modulating their stability under generalphysiological conditions (pH=7.5±0.5) and at lysosomal pH (pH near 5).For example, hydrolysis of ketal groups is known to be catalyzed byacids, therefore polyketals will be in general less stable in acidiclysosomal environment than, for example, in blood plasma. One can designa test to compare polymer degradation profile at, for example, pH=5 andpH=7.5 at 37° C. in aqueous media, and thus to determine the expectedbalance of polymer stability in normal physiological environment and inthe “digestive” lysosomal compartment after uptake by cells. Polymerintegrity in such tests can be measured, for example, by size exclusionHPLC. In many cases, it will be preferable that at pH=7.5 the effectivesize of the polymer will not detectably change over 1 to 7 days, andremain within 50% from the original for at least several weeks. At pH=5,on the other hand, the polymer should preferably detectably degrade over1 to 5 days, and be completely transformed into low molecular weightfragments within a two-week to several-month time frame. Although fasterdegradation may be in some cases preferable, in general it may be moredesirable that the polymer degrades in cells with the rate that does notexceed the rate of metabolization or excretion of polymer fragments bythe cells.

In certain embodiments of the present invention, the biodegradablebiocompatible polyketals can form linear or branched structures. Thebiodegradable biocompatible polyketal of the present invention can bechiral (optically active). Optionally, the biodegradable biocompatiblepolyketal of the present invention can be racemic.

Structure, yield and molecular weight of the resultant polyaldehydedepend on the initial polysaccharide. Polysaccharides that do notundergo significant depolymerization in the presence of glycol-specificoxidizing agents, for example, poly (2,1) and (2,6) fructoses, arepreferable. Examples of suitable polysaccharides include alpha and beta2,1 and 2,6 fructans. Particularly preferred polysaccharides are Inulin,Levans from plants, and bacterial fructans. Examples of suitableglycol-specific oxidizing agents include sodium periodate, leadtetra-acetate, periodic acid, etc. In certain embodiments, the oxidationsystem consists of a non-specific oxidizing agent in combination withglycol-specific catalyst or and intermediate oxidizer, or anelectrochemical cell. Examples of suitable reducing agents includesodium borohydride, sodium cyanoborohydride, etc. Temperature, pH andreaction duration can affect the reaction rate and polymer hydrolysisrate. The reaction is preferably conducted in the absence of light. Oneskilled in the art can optimize the reaction conditions to obtainpolymers of desired composition. The resultant polymeric aldehydeintermediate may be reduced to the corresponding alcohol via a suitablereducing agent. Alternatively, aldehyde groups can be conjugated with avariety of compounds or converted to other types of functional groups.In certain preferred embodiments, under physiological conditions, atleast one of the aldehyde groups in the aldehyde-substituted polyketalcan exist in a hydrated (hem-diol) form. As such, the aldehyde group isconsidered a hydrophilic group. In another embodiment, the precursorcarbohydrate has a chiral atom outside of the cleavage site. Thus thechirality of that atom is retained, and the polyketal is chiral oroptically active.

In certain embodiments, the polyketals of the present invention cancontain intermittent irregularities throughout the polyketal, such asincompletely oxidized additional groups or moieties in the main chain orin the side chains, as shown below:

wherein k, m, and n are integers greater than or equal to one.

Although it is generally understood that each ketal unit in a polyketalof the present invention can have different R¹, R², R³, R⁴, R⁵ and R⁶groups, in a preferred embodiment, more than 50% of the ketal units havethe same R¹, R², R³, R⁴, R⁵, and R⁶. For example, preferred polyacetalsof this invention include polymers of the general formula:

in which 1 to 50% of hydroxyls may further be conjugated with moietieswhich are either hydrophilic, or pharmaceutically useful. These moietiescan be the same (for example, a polyketal conjugated with a drug, suchas taxol) or different (for example, a polyketal conjugated with morethan one drug, such as taxol and camptothecin, and a targeting moiety,such as a an antibody or a fragment thereof, or a receptor ligand, suchas peptide, an oligosaccharide, etc.).

Since it is believed that oxidation does not affect configurations at C¹and C², the aldehyde intermediate and the polyketal retain theconfiguration of the parent polysaccharide, and the polyketals can thusbe formed in stereoregular isotactic forms.

Fully Synthetic Route

In another preferred embodiment, the biodegradable biocompatiblepolyketals of the present invention can be prepared by reacting asuitable initiator with a precursor compound comprising the chemicalstructure:

which forms a polymer intermediate comprising the chemical structure:

wherein each occurrence of P¹ and P² includes a carbon atom covalentlyattached to C¹ and is independently an organic moiety or a protectedorganic moiety; P^(x) includes a carbon atom covalently attached to C²;n is an integer; each occurrence of P³, P⁴, P⁵ and P⁶ is independentlyhydrogen, an organic moiety or a protected organic moiety. For eachoccurrence of the bracketed structure n, at least one of P¹, P², P³, P⁴,P⁵ and P⁶ is either a protected hydrophilic group, or a pharmaceuticallyuseful group. In a preferred embodiment, P¹, P², P³, P⁴, P⁵ and P⁶ donot prevent polymerization. Furthermore, P¹, P², P³, P⁴, P⁵ and P⁶ aresuitable for conversion to hydrophilic groups as described above. In oneembodiment, when appropriate, the protected hydrophilic groups orprotected organic moieties of the polymer intermediate are deprotectedand optionally derivatized, thereby forming the polyketal comprising thestructure:

wherein R¹ and R² are biocompatible groups and include a carbon atomcovalently attached to C¹; R^(x) includes a carbon atom covalentlyattached to C²; n is an integer; each occurrence of R³, R⁴, R⁵ and R⁶ isa biocompatible group and is independently hydrogen or an organicmoiety; and at least one of R¹, R², R³, R⁴, R⁵ and R⁶ is eitherhydrophilic or pharmaceutically useful. Alternatively, other ringopening techniques can be employed or developed, for example employingappropriate catalysts and resulting in the formation of polyketalscomprising unsaturated linkages within the main chain. The latter can befurther transformed into single bonds using appropriate reagents. Thus,in certain embodiments, a method for forming a biodegradablebiocompatible polyketal, comprises steps of: a) reacting a suitableinitiator with a compound having the chemical structure:

thereby forming a polymer intermediate comprising the chemicalstructure:

wherein each occurrence of P¹ and P² is independently an organic moietyor a protected organic moiety and includes a carbon atom covalentlyattached to C¹; each occurrence of P^(x) is an organic moiety andincludes a carbon atom covalently attached to C²; n is an integer; eachoccurrence of P³, P⁴, P⁵ and P⁶ is independently hydrogen, an organicmoiety or a protected organic moiety; and for each occurrence of thebracketed structure n, at least one of P¹, P², P³, P⁴, P⁵ and P⁶ is aprotected hydrophilic group or a pharmaceutically useful group; b)optionally reacting said polymer intermediate with a suitable reagentunder suitable conditions to form second polymer intermediate; and c)optionally repeating step b) until the desired functionalization of saidpolymer intermediate is achieved; thereby forming a polyketal comprisingthe structure:

wherein each occurrence of R¹ and R² is independently a biocompatiblegroup and includes a carbon atom covalently attached to C¹; eachoccurrence of R^(x) includes a carbon atom covalently attached to C²; nis an integer; each occurrence of R³, R⁴, R⁵ and R⁶ is a biocompatiblegroup and is independently hydrogen or an organic moiety; and for eachoccurrence of the bracketed structure n, at least one of R¹, R², R³, R⁴,R⁵ and R⁶ is a hydrophilic group or a pharmaceutically useful group.

“Protected hydrophilic group” and “Protected organic moiety” as theseterms are used herein, mean a chemical group which will not interferewith decyclization of the precursor compound by the initiator or preventsubsequent polymerization, and which, upon additional treatment by asuitable agent, can be converted to a hydrophilic functional group or anorganic moiety, respectively. Examples of protected hydrophilic groupsinclude carboxylic esters, alkoxy groups, thioesters, thioethers, vinylgroups, haloalkyl groups, Fmoc-alcohols, etc.

Examples of suitable organic moieties include, but are not limited to,hydroxyl, hydroxyalkyl, amine, carboxyl, amide, carboxylic ester,thioester, aldehyde, nitryl, isonitryl, nitroso, hydroxylamine,mercaptoalkyl, heterocycle, carbamates, carboxylic acids and theirsalts, sulfonic acids and their salts, sulfonic acid esters, phosphoricacids and their salts, phosphate esters, polyglycol ethers, polyamines,polycarboxylates, polyesters, polythioesters, pharmaceutically usefulgroups, a biologically active substance or a diagnostic label.

In certain preferred embodiments, the biodegradable biocompatiblepolyketals of the present invention can be chemically modified by, forexample, crosslinking the polyketals to form a gel. The crosslinkdensity of the biodegradable biocompatible polyketal is generallydetermined by the number of reactive groups in the polyketal and by thenumber of crosslinking molecules, and can be controlled by varying theratio of polyketal to the amount of crosslinker present. Thus, incertain embodiments, the invention provides a method for forming acrosslinked biodegradable biocompatible polyketal, comprising steps of:a) reacting an effective amount of an oxidizing agent with apolysaccharide to form an aldehyde intermediate; b) optionally treatingthe biodegradable biocompatible polyketal aldehyde formed in step (a)with a suitable reagent under suitable conditions to form a polyketalpolymer intermediate; c) optionally repeating step b) until the desiredfunctionalization of said polyketal polymer intermediate is achieved;and d) reacting said polyketal polymer intermediate with a crosslinkingagent.

In one embodiment, a suitable crosslinking agent has the formulaX¹—(R)—X², where R is a spacer group and X¹ and X² are reactive groups.The spacer group R may be an aliphatic, alicyclic, heteroaliphatic,heteroalicyclic, aryl or heteroaryl moiety. Examples of suitable spacergroups include biodegradable or nonbiodegradable groups, for example,aliphatic groups, carbon chains containing biodegradable inserts such asdisulfides, esters, etc. The term “reactive group,” as it relates to X¹and X², means functional groups which can be connected by a reactionwithin the biodegradable biocompatible polyketals, thereby crosslinkingthe biodegradable biocompatible polyketals. Suitable reactive groupswhich form crosslinked networks with the biodegradable biocompatiblepolyketals include epoxides, halides, tosylates, mesylates,carboxylates, aziridines, cyclopropanes, esters, N-oxysuccinimideesters, disulfides, anhydrides etc.

In one of the preferred embodiments of the present invention, thebiodegradable biocompatible polyketals are crosslinked withepibromohydrin or epichlorohydrin. More preferably, the epibromohydrinor epichlorohydrin is present in an amount in the range of between aboutone and twenty five percent by weight of the crosslinked biodegradablebiocompatible polyketals.

Alternatively, the term “reactive” group as it relates to X¹ and X²means a nucleophilic group that can be reacted with an aldehydeintermediate of the biodegradable biocompatible polyketals, therebycrosslinking the biodegradable biocompatible polyketals. In certainembodiments, the invention provides a method for forming a crosslinkedbiodegradable biocompatible polyketal, comprising steps of: a) reactingan effective amount of an oxidizing agent with a polysaccharide to forman aldehyde intermediate; b) optionally treating the biodegradablebiocompatible polyketal aldehyde formed in step (a) with a suitablereagent under suitable conditions to form a polyketal polymerintermediate; c) optionally repeating step b) until the desiredfunctionalization of said polyketal polymer intermediate is achieved;and d) reacting said polyketal polymer intermediate with a crosslinkingagent.

In certain other embodiments, a method for forming a crosslinkedbiodegradable biocompatible polyketal comprises steps of: a) reacting aneffective amount of an oxidizing agent with a polysaccharide to form analdehyde intermediate; and b) reacting said aldehyde intermediate with acrosslinking agent.

In certain other embodiments, a method for forming a crosslinkedbiodegradable biocompatible polyketal comprises steps of: a) reacting asuitable initiator with a compound having the chemical structure:

thereby forming a polymer intermediate comprising the chemicalstructure:

wherein each occurrence of P¹ and P² is independently an organic moietyor a protected organic moiety and includes a carbon atom covalentlyattached to C¹; each occurrence of P^(x) is an organic moiety whichincludes a carbon atom covalently attached to C²; n is an integer; eachoccurrence of P³, P⁴, P⁵ and P⁶ is independently hydrogen, an organicmoiety or a protected organic moiety; and for each occurrence of thebracketed structure n, at least one of P¹, P², P³, P⁴, P⁵ and P⁶ is aprotected hydrophilic group or a pharmaceutically useful group; b)optionally reacting said polymer intermediate with a suitable reagentunder suitable conditions to form second polymer intermediate; c)optionally repeating step b) until the desired functionalization of saidpolymer intermediate is achieved; and d) reacting the biodegradablebiocompatible polyketal formed in step c) with a crosslinking agent.

Suitable reactive groups for the aldehyde intermediate include amines,thiols, polyols, alcohols, ketones, aldehydes, diazocompounds, boronderivatives, ylides, isonitriles, hydrazines and their derivatives andhydroxylamines and their derivatives, etc.

In certain embodiments, the biodegradable biocompatible polyketal can becombined with a suitable aqueous base, such as sodium hydroxide, andcrosslinked with epibromohydrin. Control of the amounts ofepibromohydrin can determine the degree of crosslinking within thebiodegradable biocompatible polyketal gel. For example, biodegradablebiocompatible polyketals can be exposed to varying amounts ofepibromohydrin for a period of about eight hours at a temperature about80° C. to form crosslinked biodegradable biocompatible polyketal gelswhich vary in crosslink density in relation to the amount ofepibromohydrin utilized. The crosslinked biodegradable biocompatiblepolyketal gel can further be reacted with a drug.

Treatment of the biodegradable biocompatible polyketal with a suitablebase, such as triethylamine in dimethylsulfoxide (DMSO), and ananhydride provides, for example, a derivatized polyketal solution.Control of the amount of anhydride within the biodegradablebiocompatible polyketal can determine the degree of derivitization ofthe polyketal in the solution.

In another embodiment of the present invention, treatment of polylysinelabeled with DPTA (diethylenetriaminepentaacetic acid) with thebiodegradable biocompatible polyketal aldehyde, in water, for example,followed by subsequent reduction in water, provides a derivatizedpolyketal solution.

Polyketals of this invention can have a variety of functional groupsthat can be readily derivatized. For example, aldehyde groups of anintermediate product of polysaccharide oxidation can be converted notonly into alcohol groups, but also into amines, thioacetals, carboxylicacids, amides, esters, thioesters, etc.

In certain embodiments, terminal groups of the polymers of thisinvention can differ from R¹, R², R³, R⁴, R⁵ or R⁶. Terminal groups canbe created, for example, by selective modification of each reducing andnon-reducing terminal unit of the precursor polysaccharide. One skilledin the art can utilize known chemical reactions to obtain desiredproducts with varying terminal groups. For example, a hemiketal group atthe reducing end of a polyketose can be readily and selectivelytransformed into a carboxylic acid group (e.g., via formation of acarboxyl-substituted glycoside) and further into a variety of otherfunctional groups.

In one embodiment, the terminal group is such that it allows binding ofthe polymeric chain to a solid support either directly or via a suitablelinker. This has the advantage of allowing solid phase chemicalmodification of the immobilized polymer to the desired polyketal of theinvention. Benefits of this technique include ease of purification byfiltration, use of excess reagent for driving reactions to completion,and ease of automation. Examples of suitable solid support arepolystyrene, polyethylene glycol, cellulose, controlled pore-glass, etc.. . . . Examples of suitable linkers are those that can be cleaved underneutral or basic conditions, such as ester or sulfide linkages.

In one embodiment, the polyketal of the present invention is associatedwith at least one small molecule, a pharmaceutically useful group, adrug, a macromolecule or a diagnostic label. Examples of suitable drugmolecules comprise a biologically active functional group fragment ormoiety. Specific examples of suitable drug molecules include vitamins,anti-AIDS substances, anti-cancer substances, antibiotics,immunosuppressants, anti-viral substances, enzyme inhibitors,neurotoxins, opioids, hypnotics, anti-histamines, lubricants,tranquilizers, anti-convulsants, muscle relaxants and anti-Parkinsonsubstances, anti-spasmodics and muscle contractants including channelblockers, miotics and anti-cholinergics, anti-glaucoma compounds,anti-parasite and/or anti-protozoal compounds, modulators ofcell-extracellular matrix interactions including cell growth inhibitorsand anti-adhesion molecules, vasodilating agents, inhibitors of DNA, RNAor protein synthesis, anti-hypertensives, analgesics, anti-pyretics,steroidal and non-steroidal anti-inflammatory agents, anti-angiogenicfactors, anti-secretory factors, anticoagulants and/or antithromboticagents, local anesthetics, ophthalmics, prostaglandins,anti-depressants, anti-psychotic substances, anti-emetics, and imagingagents.

Examples of pharmaceutically useful groups include, but are not limitedto hydrophilicity/hydrophobicity modifiers, pharmacokinetic modifiers,antigens, receptor ligands, nucleotides, chemotherapeutic agents,antibacterial agents, antiviral agents, immunomodulators, hormones andtheir analogs, enzymes, inhibitors, alkaloids, therapeuticradionuclides, etc. Suitable chemotherapeutic compounds are, forexample, topoisomerase I and II inhibitors, alkylating agents,anthracyclines, doxorubicin, cisplastin, carboplatin, vincristine,mitromycine, taxol, camptothecin, antisense oligonucleotides, ribozymes,dactinomycines, etc. Other suitable compounds include therapeuticradionuclides, such as β-emitting isotopes of rhenium, cesium, iodine,and alkaloids, etc. In one embodiment of the present invention, at leastone of R¹, R², R³, R⁴, R⁵ and R⁶ contains doxorubicin.

In another embodiment of the present invention, in at least one ketalunit at least one of R¹, R², R³, R⁴, R⁵ and R⁶ comprises a diagnosticlabel. Examples of suitable diagnostic labels include diagnosticradiopharmaceutical or radioactive isotopes for gamma scintigraphy andPET, contrast agent for Magnetic Resonance Imaging (MRI) (for exampleparamagnetic atoms and superparamagnetic nanocrystals), contrast agentfor computed tomography, contrast agent for X-ray imaging method, agentfor ultrasound diagnostic method, agent for neutron activation, andmoiety which can reflect, scatter or affect X-rays, ultrasounds,radiowaves and microwaves, fluorophores in various optical procedures,etc. Diagnostic radiopharmaceuticals include γ-emitting radionuclides,e.g., indium-111, technetium-99m and iodine-131, etc. Contrast agentsfor MRI (Magnetic Resonance Imaging) include magnetic compounds, e.g.paramagnetic ions, iron, manganese, gadolinium, lanthanides, organicparamagnetic moieties and superparamagnetic compounds, e.g., iron oxidecolloids, ferrite colloids, etc. Contrast agents for computed tomographyand other X-ray based imaging methods include compounds absorbingX-rays, e.g., iodine, barium, etc. Contrast agents for ultrasound basedmethods include compounds which can absorb, reflect and scatterultrasound waves, e.g., emulsions, crystals, gas bubbles, etc. Stillother examples include substances useful for neutron activation, such asboron. Further, substituents can be employed which can reflect, scatter,or otherwise affect X-rays, ultrasound, radiowaves, microwaves and otherrays useful in diagnostic procedures. In a preferred embodiment, atleast one of R¹, R² and R³ comprises a paramagnetic ion or group.

In yet another embodiment, the polyketals of the present invention areassociated with a macromolecule. Examples of suitable macromoleculesinclude, but are not limited to, proteins, enzymes, growth factors,cytokines, peptides, polypeptides, polylysine, proteins, lipids, DNA,RNA, polyelectrolytes, antibodies, and lectins. The macromolecule may bechemically modified prior to being associated with said biodegradablebiocompatible polyketal.

Biodegradable Polyketal Compositions

In certain embodiments, there is provided a composition comprising themacromolecular product of the lateral cleavage of a polysaccharide;whereby at least one carbon-carbon bond is cleaved in substantially allthe carbohydrate moieties of said polysaccharide. In certain exemplaryembodiments, the lateral cleavage is effected using an oxidizing agent.In certain other exemplary embodiments, the oxidizing agent is aglycol-specific agent. In still other embodiments, the glycol-specificagent is sodium periodate.

In yet other embodiments, the invention provides a compositioncomprising the macromolecular product of the lateral cleavage of apolysaccharide; whereby at least one carbon-carbon bond is cleaved insubstantially all the carbohydrate moieties of said polysaccharide;wherein the macromolecular product is obtained by any one of the methodsdescribed herein.

In certain embodiments, the invention provides a composition in the formof a gel of the biodegradable biocompatible ketal and a biologicallyactive compound disposed within the gel. Alternatively or additionally,a diagnostic label can be disposed within the gel or bound to the gelmatrix.

In another embodiment, the invention provides a composition in the formof a solution of the biodegradable biocompatible polyketal and apharmaceutically useful entity, a drug or a macromolecule dissolvedwithin the solution. Alternatively or additionally, a diagnostic labelcan be dissolved within the solution.

In certain embodiments, there is provided a composition comprising abiodegradable biocompatible polyketal of the invention associated withan effective amount of a therapeutic agent; wherein the therapeuticagent is incorporated into an released from said biodegradablebiocompatible polyketal matrix by degradation of the polymer matrix ordiffusion of the agent out of the matrix over a period of time. Incertain embodiments, the therapeutic agent is selected from the groupconsisting of vitamins, anti-AIDS substances, anti-cancer substances,antibiotics, immunosuppressants, anti-viral substances, enzymeinhibitors, neurotoxins, opioids, hypnotics, anti-histamines,lubricants, tranquilizers, anti-convulsants, muscle relaxants andanti-Parkinson substances, anti-spasmodics and muscle contractantsincluding channel blockers, miotics and anti-cholinergics, anti-glaucomacompounds, anti-parasite and/or anti-protozoal compounds, modulators ofcell-extracellular matrix interactions including cell growth inhibitorsand anti-adhesion molecules, vasodilating agents, inhibitors of DNA, RNAor protein synthesis, anti-hypertensives, analgesics, anti-pyretics,steroidal and non-steroidal anti-inflammatory agents, anti-angiogenicfactors, anti-secretory factors, anticoagulants and/or antithromboticagents, local anesthetics, ophthalmics, prostaglandins,anti-depressants, anti-psychotic substances, anti-emetics, imagingagents, and combination thereof.

In variations of these embodiments, it may be desirable to include otherpharmaceutically active compounds, such as antiinflammatories orsteroids which are used to reduce swelling, antibiotics, antivirals, orantibodies. Other compounds which can be included are preservatives,antioxidants, and fillers, coatings or bulking agents which may also beutilized to alter polymer matrix stability and/or drug release rates.

Additives Used to Alter Properties of Polymeric Compositions:

In a preferred embodiment, only polyketal and drugs to be released areincorporated into the delivery device or construct, although otherbiocompatible, preferably biodegradable or metabolizable, materials canbe included for processing, preservation and other purposes.

Buffers, acids and bases are used to adjust the pH of the composition.Agents to increase the diffusion distance of agents released from theimplanted polymer can also be included.

Fillers are water soluble or insoluble materials incorporated into theformulation to add bulk. Types of fillers include sugars, starches andcelluloses. The amount of filler in the formulation will typically be inthe range of between about 1 and about 90% by weight.

Biodegradable Biocompatible Polyketals—Methods of Use

The present invention encompasses highly regular, biodegradable polymersfor use in biomedical applications, primarily (but not exclusively) inthe fields of pharmacology, bioengineering, wound healing, anddermatology/cosmetics. In particular, medical applications for thebiocompatible biodegradable polymers of the invention include tabletcoatings, plasma substitutes, gels, contact lenses, surgical implants,systems for controlled drug release, as ingredients of eyedrops, woundclosure applications (sutures, staples), orthopedic fixation devices(pins, rods, screws, tacks, ligaments), dental applications (guidedtissue regeneration), cardiovascular applications (stents, grafts),intestinal applications (anastomosis rings), and as long circulating andtargeted drugs. Biodegradable biocompatible polyketals of the presentinvention can be employed as components of biomaterials, drugs, drugcarriers, pharmaceutical formulations, medical devices, implants, andcan be associated with small molecules, pharmaceutically usefulentities, drugs, macromolecules and diagnostic labels.

Methods of Treating

In certain preferred embodiments of the invention, the polyketals areused in methods of treating animals (preferably mammals, most preferablyhumans). In one embodiment, the polyketals of the present invention maybe used in a method of treating animals which comprises administering tothe animal the biodegradable biocompatible polyketal. For example,polyketals in accordance with the invention can be administered in theform of soluble linear polymers, copolymers, conjugates, colloids,particles, gels, solid items, fibers, films, etc. Biodegradablebiocompatible polyketals of this invention can be used as drug carriersand drug carrier components, in systems of controlled drug release,preparations for low-invasive surgical procedures, etc. Pharmaceuticalformulations can be injectable, implantable, etc.

In one embodiment, a method of administering to a patient in need oftreatment comprises administering to the subject an effective amount ofa suitable therapeutic agent; wherein the therapeutic agent isincorporated into and released from biodegradable biocompatiblepolyketal matrix by degradation of the polymer matrix or diffusion ofthe agent out of the matrix over a period of time.

In another embodiment, the therapeutic agent can be locally delivered byimplantation of the biodegradable biocompatible polyketal matrixassociated with the therapeutic agent.

In yet another embodiment, additional biologically active compounds canbe administered with the polymer-associated therapeutic agent. Examplesof biologically active compounds include chemotherapeutics,antiinflammatories, anti-AIDS substances, anti-cancer substances,antibiotics, immunosuppressants, anti-viral substances, enzymeinhibitors, neurotoxins, opioids, hypnotics, anti-histamines,lubricants, tranquilizers, anti-convulsants, muscle relaxants andanti-Parkinson substances, anti-spasmodics and muscle contractantsincluding channel blockers, miotics and anti-cholinergics, anti-glaucomacompounds, anti-parasite and/or anti-protozoal compounds, modulators ofcell-extracellular matrix interactions including cell growth inhibitorsand anti-adhesion molecules, vasodilating agents, inhibitors of DNA, RNAor protein synthesis, anti-hypertensives, analgesics, anti-pyretics,steroidal and non-steroidal anti-inflammatory agents, anti-angiogenicfactors, anti-secretory factors, anticoagulants and/or antithromboticagents, local anesthetics, ophthalmics, prostaglandins,anti-depressants, anti-psychotic substances, anti-emetics, imagingagents, and combinations thereof.

In one embodiment, a method for treating an animal comprisesadministering to the animal the biodegradable biocompatible polyketal ofthe invention as a packing for a surgical wound from which a tumor orgrowth has been removed. The biodegradable biocompatible polyketalpacking will replace the tumor site during recovery and degrade anddissipate as the wound heals.

In certain embodiments, the polyketal is associated with a diagnosticlabel for in vivo monitoring.

Applications to Drug Delivery Methods

Polyketal—small-molecule-drug conjugates: In one embodiment,pharmaceutical agents are associated with the biodegradablebiocompatible polyketal to form a biodegradable biocompatible gel ormass of polyketal in which the drug is entrapped or bound to gel matrix,or a soluble conjugate of a drug and a polyketal. This can be achieved,for example, by coupling the polyketal with a drug (for example, taxolor camptothecin (CPT)). Alternatively, the drug can be entrapped bydissolution of the drug in the presence of the biodegradablebiocompatible polyketal during removal of a solvent, or duringcrosslinking. When soluble ketal-drug conjugates are administered (e.g.,injected) into an animal, they can circulate and accumulate at adesirable site, and slowly resease the drug either in circulation, or atthe accumulation site, either intracellularly or extracellularly. Whengels or masses are implanted into an animal, slow hydrolysis of thebiodegradable biocompatible polyketal mass or gel occurs with continuousslow release of the agent in the animal at the location where itsfunction is required. Such polymer-drug pharmaceutical compositions mayafford release of the physiologically active substance intophysiological fluids in vivo over a sustained period (for an example ofpolymer-drug conjugate, see Li, et al. “Water soluble paclitaxelprodrugs” U.S. Pat. No. 6,262,107, 2001, the entire contents of whichare incorporated herein by reference). In addition, the hydrophilicpolyketals of the invention may be used to stabilize drugs, as well asto solubilize otherwise insoluble compounds. For example, Paclitaxel, ananti-microtubule agent that has shown a remarkable anti-neoplasticeffect in human cancer in Phase I studies and early Phase II and IIItrials (Horwitz et al., “Taxol, mechanisms of action and resistance,” J.Natl. Cancer Inst. Monographs No. 15, pp. 55-61, 1993), has limitedsolubility in water, which has hampered its development for clinicaltrial use. The polyketal-drug pharmaceutical compositions of theinvention could provide water soluble taxoids to overcome the drawbacksassociated with the insolubility of the drugs themselves, and alsoprovide the advantages of accumulation in tumors, targeting to cancercells and controlled release so that tumors may be eradicated moreefficiently. Association of chemotherapeutic drugs to the polyketals ofthe invention may also be an attractive approach to reduce systemictoxicity and improve the therapeutic index. In particular, it is knownin the art that polymers with molecular mass larger than 30 kDa do notreadily diffuse through normal capillaries and glomerular endothelium,thus sparing normal tissue from irrelevant drug-mediated toxicity (Maedaand Matsumura, “Tumoritropic and lymphotrophic principles ofmacromolecular drugs”, Critical Review in Therapeutic Drug CarrierSystems, 6:193-210, 1989; Reynolds, T., “Polymers help guide cancerdrugs to tumor targets- and keep them there,” J. Natl. Cancer Institute,87:1582-1584, 1995). On the other hand, it is well established thatmalignant tumors often have altered capillary endothelium and greaterpermeability than normal tissue vasculature (Maeda and Matsumura, 1989;Fidler, et al., “The biology of cancer invasion and metastasis,” Adv.Cancer Res., 28:149-250, 1987). Thus, a polymer-drug conjugate, such asthose described in the present invention, that would normally remain inthe vasculature, may selectively leak from blood vessels into tumors,resulting in tumor accumulation of active therapeutic drug. The methodsdescribed herein could also be used to make water soluble polyketalcomplexes of other therapeutic agents, contrast agents and drugs.

Polyketal-modified proteins: In certain embodiments, the polyketals maybe associated to a protein or peptide (for example enzymes or growthfactors) to form a polyketal-modified protein/peptide. Improved chemicaland genetic methods have made many enzymes, proteins, and other peptidesand polypeptides available for use as drugs or biocatalysts havingspecific catalytic activity. However, limitations exist to the use ofthese compounds. For example, enzymes that exhibit specific biocatalyticactivity sometimes are less useful than they otherwise might be becauseof problems of low stability and solubility. During in vivo use, manyproteins are cleared from circulation too rapidly. Some proteins haveless water solubility than is optimal for a therapeutic agent thatcirculates through the bloodstream. Some proteins give rise toimmunological problems when used as therapeutic agents. Immunologicalproblems have been reported from manufactured proteins even where thecompound apparently has the same basic structure as the homologousnatural product. The use of polymer-modified proteins or peptides mayhelp protect the protein/peptide from chemical attack, limit its adverseside effects when injected into the body, increase its size, and maythus potentially improve its therapeutic profile in vivo (e.g., safety,efficacy and stability in biological media). See for example Harris etal. “Multiarmed, monofunctional, polymer for coupling to molecules andsurfaces” U.S. Pat. No. 5,932,462, 1999. Examples of proteins that maybe used in this context are enzymes, recognition proteins, carrierproteins, and signaling proteins and polypeptides, such as, urokinase,catalase, hemoglobin, granulocyte colony stimulating factor (G-CSF),interferons, cytokines, leptins, insulin, etc.

Although there is no theory that predicts the optimal composition, sizeand shape of a macromolecule conjugate, it can be expected that, forsome applications, conjugates consisting of one protein molecule and onepolyketal molecule will be preferable, whereas in other applicationsconjugates comprising several identical or different protein or peptidemolecules per polyketal molecule can be preferable. In one preferredembodiment, a protein is conjugated with a polyketal of the inventionvia a terminal group of the latter. In another embodiment, one or moreprotein or peptide molecules are conjugated to the polyketal molecule ofthe invention at random points.

Cationized polyketal: In another embodiment, the polyketals of thepresent invention may find use as a nucleic acid carrier vehicle fordelivery of nucleic acid material to target cells in biological systems(for example in applications using adducts with DNA orPolyketal-modified virus). Such material may find applications for invivo delivery of genes or therapeutic DNA to a patient in carrying outgene therapy or DNA vaccination treatment (See for example Schacht etal. “Delivery of nucleic acid material” U.S. Pat. No. 6,312,727, 2001;German et al. “Enhanced adenovirus-assisted transfection composition andmethod” U.S. Pat. No. 5,830,730, 1998). For example, the polyketal maybe synthesized or modified so as to form a “cationized” material wherebyone or more cationic sites are included or incorporated in the polyketalmolecule. Association or binding of this cationized hydrophilic polymerwith a polyanionic nucleic acid component results in a material that mayfunction as a DNA or nucleic acid delivery device. The nucleic acidcomponent may comprise a polynucleotide, plasmid DNA, lineardouble-helical DNA, RNA or a virus. In another embodiment, the cationicpolyketal core may be associated, directly or indirectly, to othermolecular entities or moieties, especially bioactive molecules, thatmodify the biological and/or physico-chemical characteristics of thecomplex to improve suitability or specificity for use in delivering thenucleic acid material to target cells. These other molecular entities ormoieties may comprise cell-receptor targeting moieties and/or otherspecific bioactive agents providing, for example, membrane disruptingagents, agents capable of promoting endocytic internalization followingbinding to cell surface molecules, and nuclear-homing agents, useful forfacilitating entry and delivery of the nucleic acid material, e.g. DNA,into cells.

Polyketal-modified liposomes: In yet another embodiment, the polyketalsof the present invention may be associated with a liposome (see forexample Dadey “Polymer-associated liposomes for drug delivery and methodof manufacturing the same” U.S. Pat. No. 5,935,599, 1999). In certainembodiments, the polyketal-associated liposome is formulated with a drugor a therapeutic agent to provide a drug composition that treats anunderlying disease or complications associated with the disease. Thepolyketal-associated liposome may be formulated with eitherwater-soluble or water-insoluble drugs, or both. Therefore, a drugcomposition containing a polyketal-associated liposome and a drug can beadministered in a variety of dosage forms. A liposome is a mono- ormultilamellar vesicle prepared from a phospholipid or other suitablelipids or mixtures thereof. Structurally, lamellae are bilayer membraneshaving polar ends of lipids in one layer forming the external surface ofthe spherical membrane and the polar ends of lipids in a second layerforming the internal surface of the spherical membrane. Membranes caninclude hydrophobic additives, such as cholesterol. The nonpolar,hydrophobic tails of the lipids in the two layers self-assemble to formthe interior of the bilayer membrane. Liposomes can microencapsulatecompounds, and transport the compounds through environments wherein theyare normally degraded. The liposome can be prepared by conventionaltechniques from phosphatidylethanolamine, phosphatidylcholine,phosphatidylserine, phosphatidylinositol, phostidylglycerol,sphingomyelin, and mixtures thereof. The outer layer of a liposome canbe modified with a polyketal to either prevent liposome aggregation, orto prolong liposome circulation in blood, or for other purposes.Preferably, polyketal molecules are chemically linked to lipid moleculesconstituting the outer membrane. Some or all polyketal molecules can befurther modified with targeting moieties that assist liposome binding totarget cells or tissues. In a preferred embodiment, polyketal moleculesare linked to lipid molecules through terminal groups, forminglipid-polyketal conjugates. The latter can be incorporated intoliposomes during the process of liposome formation, e.g. by extrusion.Alternatively, polyketals can be chemically bound to pre-formedliposomes comprising suitable functional groups on the outer surface(e.g., amino, mercapto, or carboxygroups).

Polyketal-modified nano- and microparticles: In a further embodiment ofthe present invention, the polyketals may be designed so as to haveproperties suitable for manufacturing by various processes intonanoparticles, microparticles and microspheres for applications in drugdelivery systems. Polyketals can be utilized in such applications asinterface components, particle matrix components, or both. Wherepolyketals are used as interface components, the (inner) particle can bea nanoparticle (e.g., iron oxide nanocrystal or combination thereof), alatex particle (e.g., polystyrene nanosphere or microsphere), a gelparticle (e.g., crosslinked polyketal or polysaccharide gel sphere),etc. Where the polyketal is used as a matrix component, alone or alongwith other macromolecular components or particulates, the polyketalmolecules can be chemically crosslinked or non-chemically associated toform a gel or a solid, and can be chemically or physically associatedwith a drug. The latter becomes, therefore, incorporated or entrapped inthe particle, and can subsequently be released via diffusion ordegradation mechanisms.

The slow-release characteristic of the polymer microparticles may alsohave use in the field of pharmacology where the microparticles can beused, for example, to deliver pharmacological agents in a slow andcontinual manner (see for example Sokoll et al. “Biodegradabletargetable microparticle delivery system” U.S. Pat. No. 6,312,732,2001). A wide range of drugs such as anti-hypertensives, analgesics,steroids and antibiotics can be used in accordance with the presentinvention to provide a slow release drug delivery system. Largemolecules, such as proteins, can also be entrapped in micro- andnanoparticles, using methods of particle formation that do notinactivate the large molecule. Microspheres may be prepared by knownmethods in the art, for example, using a single emulsification process(U.S. Pat. No. 4,389,330 to Tice et al.; U.S. Pat. No. 3,691,090 toKitajima et al.), a double emulsification process (Edwards et al.,Science 276: 1868-1871, 1997), a phase inversion microencapsulationprocess (Mathiowitz et al., Nature 386: 410-413, 1997), or anatomization-freeze process (Putney and Burke, Nature Biotechnology 16:153-157, 1998). In the single emulsification process, a volatile organicsolvent phase containing a biodegradable polymer, an aqueous solutioncontaining an emulsifier such as polyvinyl alcohol, and aphysiologically active substance are homogenized to produce an emulsion.The solvent is evaporated and the resulting hardened microspheres arefreeze-dried. In the double emulsification process, an aqueous solutionwhich may contain a physiologically active substance and a volatileorganic solvent phase containing a biodegradable polymer are homogenizedto form an emulsion. The emulsion is mixed with another aqueoussolution, which contains an emulsifier such as polyvinyl alcohol.Evaporation of the solvent and freeze-drying produces microspheres. Inthe phase inversion microencapsulation process, the drug is added to adilute polymer solution in a solvent (e.g. dichloromethane) which isthen poured rapidly into an unstirred bath of another liquid (e.g.petroleum ether) causing nano- and microspheres to form spontaneously.In the atomization-freeze process, the micronized solid physiologicallyactive substance is suspended in a solvent phase containing abiodegradable polymer that is then atomized using sonication orair-atomization. This produces droplets that are then frozen in liquidnitrogen. Addition of another solvent in which both the polymer and thedrug are insoluble extracts the solvent from the microspheres. In suchprocesses, polyketals can be used as interface components formed duringor after particle formation. Preferably, the process is engineered suchthat polyketal molecules form a monolayer on the particle surface, whichis dense enough to modify the particle surface hydrophilicity, and/or toprevent direct contact of cells and/or recognition proteins with theparticle surface. This can be achieved, for example, by chemicalcoupling of the polyketal to the surface of the pore-formed particles,or through addition of polyketal-matrix polymer conjugates intotechnological solutions. Such conjugates (e.g., block copolymers) will,in appropriately optimized conditions, incorporate into particles suchthat the matrix polymer block will incorporate into the particle body,while the polyketal block will be exposed on the particle surface.Similar approaches can be used for the modification of inorganicparticles (such as colloids and nanocrystals) with ketals during orafter their formation. Polyketals can be attached to the surfaces ofsuch particles either chemically (conjugation or grafting) or physically(adsorption). A further description of polyketal use as an interfacecomponent is given in one of the following sections.

In another embodiment, the biodegradable biocompatible polyketals of thepresent invention can be monitored in vivo by suitable diagnosticprocedures. Such diagnostic procedures include nuclear magneticresonance imaging (NMR), magnetic resonance imaging (MRI), ultrasound,X-ray, scintigraphy, positron emission tomography (PET), etc. Thediagnostic procedure can detect, for example, polyketal disposition(e.g., distribution, localization, density, etc.) or the release ofdrugs, prodrugs, biologically active compounds or diagnostic labels fromthe biodegradable biocompatible polyketals over a period of time.Suitability of the method largely depends on the form of theadministered polyketal and the presence of detectable labels. Forexample, the size and shape of polyketal implants can be determinednon-invasively by NMR imaging, ultrasound tomography, or X-ray(“computed”) tomography. Distribution of soluble polyketal preparationcomprising a gamma emitting or positron emitting radiotracer can beperformed using gamma scintigraphy or PET, respectively.Microdistribution of polyketal preparation comprising a fluorescentlabel can be investigated using photoimaging.

It is understood, for the purpose of this invention, that transfer anddisposition of polyketals in vivo can be regulated by modifying groupsincorporated into the polyketal structure or conjugated with thepolyketal, such as hydrophobic and hydrophilic modifiers, chargemodifiers, receptor ligands, antibodies, etc. Such modification, incombination with incorporation of diagnostic labels, can be used fordevelopment of new useful diagnostic agents. The latter can be designedon a rational basis (e.g., conjugates of large or small moleculesbinding known tissue components, such as cell receptors, surfaceantigens, etc.), as well as through screening of libraries of polyketalmolecules modified with a variety of moieties with unknown or poorlyknown binding activities, such as synthetic peptides andoligonucleotides, small organic and metalloorganic molecules, etc.

Interface Component

In one embodiment of the present invention, the biodegradablebiocompatible polyketal can be used as an interface component. The term“interface component” as used herein, means a component, such as acoating or a layer on an object, to alter the character of objectinteraction with biological interaction with biological milieu, forexample, to suppress foreign body reactions, decrease inflammatoryresponse, suppress clot formation, etc. It should be understood that theobject can be microscopic or macroscopic. Examples of microscopicobjects include macromolecules, colloids, vesicles, liposomes,emulsions, gas bubbles, nanocrystals, etc. Examples of macroscopicobjects include surfaces, such as surfaces of surgical equipment, testtubes, perfusion tubes, items contacting biological tissues, etc. It isbelieved that interface components can, for example, provide the objectprotection from direct interactions with cells and opsonins and, thus,to decrease the interactions of the object with the biological system.

Surfaces can be modified by the biodegradable biocompatible polyketalsof the present invention by, for example, conjugating functional groupsof the biodegradable biocompatible polyketals with functional groupspresent on the surface to be modified. For example, aldehyde groups ofthe biodegradable biocompatible polyketal precursors can be linked withamino groups by employing reducing agents or isocyanides. Alternatively,carboxyl groups of the biodegradable biocompatible polyketals can beconjugated with amino, hydroxy, sulphur-containing groups, etc. Inanother embodiment, a biodegradable biocompatible polyketal of theinvention which includes a suitable terminal group can be synthesized,such as a polyalcohol having a terminal carboxylic group. A polymer canbe connected to a surface by reaction of the terminal group. Examples ofsuitable polymers include those formed, for example, by oxidation of areducing-end acetal group into a carboxyl group, such as by using iodineor bromine. The remainder of the polysaccharide is then oxidized byemploying an effective amount of a glycol-specific oxidizing agent toform an aldehyde. The aldehydes can be selectively modified by, forexample, reduction into hydroxyl groups. The resulting polymer willgenerally have one terminal carboxyl group that can be used forone-point modification, such as by employing a carbodiimide.

In still another embodiment, a suitable polysaccharide can be linkedwith a surface by reaction of a reducing or non-reducing end of thepolysaccharide or otherwise, by subsequent oxidation and furtherconversion of the remainder of the polysaccharide to produce apolyketal.

It is to be understood that the biodegradable biocompatible polyketalsof this invention can be conjugated with macromolecules, such asenzymes, polypeptides, proteins, etc., by the methods described abovefor conjugating the biodegradable biocompatible polyketals withfunctional groups present on a surface.

The biodegradable biocompatible polyketals of the invention can also beconjugated with a compound that can physically attach to a surface via,for example, hydrophobic, van der Waals, and electrostatic interactions.For example, the biodegradable biocompatible polyketal precusors can beconjugated with lipids, polyelectrolytes, proteins, antibodies, lectins,etc.

It is believed that interface components can prolong circulation ofmacromolecular and colloidal drug carriers. Therefore, small molecules,biologically active compounds, diagnostic labels, etc., beingincorporated in such carriers, can circulate throughout the body withoutstimulating an immunogenic response and without significant interactionswith cell receptors and recognition proteins (opsonins). Further,interface components can be used to modify surfaces of implants,catheters, etc. In other embodiments of the present invention,biomedical preparations of the biodegradable biocompatible polyketal canbe made in various forms. Examples include implants, fibers, films, etc.

Chiral Polyketals

Other aspects of the present invention pertain to methods andcompositions useful in separations of stereoisomers.

The so-called “three point rule” is a commonly used rule-of-thumb inmany chiral recognition strategies. The “three point rule” recommendsthat there be a minimum of three simultaneous interactions between thechiral recognition medium and at least one of the enantiomers to beseparated. In addition, at least one of the three interactions must bestereochemically dependent. The three interactions need not beattractive interactions, and may for example employ repulsion due tosteric effects.

The three-point rule is satisfied by the novel chiral polyketals of thepresent invention, which have at least three functional groups that canyield different chiral environments: (1) the chiral center(s) in thepolysaccharide backbone; (2) the stereoregular isotactic form of thatbackbone; and (3) the pendent functional groups such as carbonyl,carboxyl, or hydroxyl, including hydrophobic interactions with sidechains.

If desired, the novel polymers may be readily crosslinked, withoutdisrupting the polymer backbone ketal links, generating stable,solvent-swollen, gels. The novel polymers may be used as astationary-phase or pseudo-stationary phase in separation techniquessuch as high performance liquid chromatography or electrokineticcapillary chromatography. The polymers are either water-soluble or theyswell in aqueous media, and are particularly useful in separations ofstereoisomers (enantiomers or diastereomers).

Chiral Polyketals

In a preferred embodiment, the polyketals of the present invention arechiral and comprise repeat structural units, wherein substantially allthe structural units comprise (i) at least one ketal group wherein atleast one ketal oxygen atom is within the polymer main chain; and (ii)at least one chiral group.

In a certain embodiment, at least a subset of the repeat structuralunits have the following structure:

wherein each occurrence of R¹ and R² is an organic moiety and includes acarbon atom or heteroatom covalently attached to C¹. R^(x) includes acarbon atom covalently attached to C². n is an integer. Each occurrenceof R³, R⁴, R⁵ and R⁶ is independently hydrogen or an organic moiety; andfor each occurrence of the bracketed structure n, at least one of C¹,C², R^(x), R¹, R², R³, R⁴, R⁵ and R⁶ is chiral.

In another embodiment of the invention, at least a subset of the repeatstructural units have the following structure:

wherein each occurrence of R² is an organic moiety and includes a carbonatom or heteroatom covalently attached to C¹; R^(x) includes a carbonatom covalently attached to C¹; n is an integer; each occurrence of R¹is an organic moiety; each occurrence of R³ and R⁴ is independentlyhydrogen or an organic moiety; and, for each occurrence of the bracketedstructure n, at least one of C¹, C², R^(x), R¹, R², R³ and R⁴ is chiral.

Each occurrence of R¹, R², R³, R⁴, R⁵ and R⁶ may be independentlyhydrophobic or hydrophilic, and may be the same or different throughoutthe polymer. Examples of organic moieties which are suitable include(but are not limited to) branched and unbranched alkyl, alkenyl,alkynyl, haloalkyl, acyl, aryl, alkylaryl, heterocyclic group,heteroaryl, alkoxy, mercaptoalkyl, amino, alkylamino, dialkylamino,trialkylamino, cyano, hydroxy, halo, mercapto, nitro, carboxyaldehyde,carboxy, alkoxycarbonyl, carboxamide, carbamates, sulfonyl, sulfoxyl,and phosphate moieties.

In a preferred embodiment of the present invention, the chiralpolyketals comprise the structure:

or are direct derivatives thereof, obtained by replacement of some orall OH or CH₂OH groups with other suitable groups.

In another preferred embodiment, the chiral polyketal of the inventioncomprise the structure:

wherein n is an integer, or are direct derivatives thereof, obtained byreplacement of some or all OH or CH₂OH groups with other suitablegroups.

In yet another embodiment, the chiral polyketals of the invention can becrosslinked. A suitable crosslinking agent has the formula X¹—(R) —X²,where R is a spacer group and X¹ and X² are reactive groups. The spacergroup R may be an aliphatic, alicyclic, heteroaliphatic,heteroalicyclic, aryl or heteroaryl moiety. Examples of suitable spacergroups include biodegradable or nonbiodegradable groups, for example,aliphatic groups, carbon chains containing biodegradable inserts such asdisulfides, esters, etc. The term “reactive group,” as it relates to X¹and X², means functional groups which can be connected by a reactionwithin the chiral polyketals, thereby crosslinking the chiralpolyketals. Suitable reactive groups which form crosslinked networkswith the chiral polyketals include epoxides, halides, tosylates,mesylates, carboxylates, aziridines, cyclopropanes, esters,N-oxysuccinimide esters, disulfides, anhydrides, substitutedhydroxylamines, hydrazines, hydrazides, etc.

Alternatively, the term “reactive” group as it relates to X¹ and X²means a nucleophilic group that can be reacted with an aldehydeintermediate of the chiral polyketals, thereby crosslinking the chiralpolyketals. Suitable reactive groups for the aldehyde intermediateinclude amines, thiols, polyols, alcohols, ketones, aldehydes,diazocompounds, boron derivatives, ylides, isonitriles, hydrazines andtheir derivatives and hydroxylamines and their derivatives, etc.

In one embodiment of the present invention, the chiral polyketals arebonded to a solid support, which imparts them improved properties. Forexample, the resistance of chiral stationary phases to pressure isimportant for their use in practice, since high flow rates are necessaryto achieve high space/time yields in the chromatographic splitting ofracemates. If the resistance to pressure is not adequate, these flowrates lead to blocking of the columns. Chiral phases which are stable topressure are obtained when the optically active material is immobilizedon an inorganic support material. Silica gels are as a rule used asinorganic support materials. The chiral polymers can be absorbed ontothese silica gels, for example, by being adsorbed physically or fixedcovalently.

One embodiment of the present invention provides chiral stationarychromatography phases comprising an inorganic support material and thechiral polyketal of the invention which is bonded to said supportmaterial either directly or via a spacer grouping. Examples of suitablesolid supports are those containing reactive groups on the surface; saidreactive groups being capable of reacting with certain functional groupson the chiral polyketal, thus effecting covalent conjugation of thechiral polymer on the solid support. Examples of suitable reactivegroups include hydroxyl, amino or sulfhydryl groups, or combinationthereof. In one embodiment of the invention, prior to conjugation withthe chiral polyketal, the solid support is chemically modified so as tocoat its surface with reactive groups suitable for reaction with saidchiral polyketal.

In one embodiment of the invention, the chiral polyketal is associatedwith a macromolecule for applications in affinity chromatography.Examples of macromolecules include, but are not limited to, receptors,enzymes, proteins and antibodies.

In one embodiment, the chiral polyketal of the invention is not 100%optically pure. Chromatography is a multi-step method where theseparation is a result of the sum of a large number of interactions.This allows for diminished requirements for the enantioselectivity ofthe stationary phase, whereby if the polyketal stationary phase containsa small quantity of the wrong isomer the effect will be countered by thecombined action of the adsorbtions along the column as a whole. It ispossible to achieve resolutions on chiral stationary phases that aresomewhat less than 100% pure. Decreasing the purity of the stationaryphase will simply decrease the enantioselectivity of the column.

Chiral Polyketals—Methods of Preparation

According to the present invention, any available techniques can be usedto make the inventive chiral polyketals or compositions including them.For example, semi-synthetic and fully synthetic methods such as thosediscussed in detail below may be used.

Semi-Synthetic Route

In a preferred embodiment, a method for forming the chiral polyketals ofthe present invention comprises a process by which a suitablepolysaccharide is combined with an effective amount of a glycol-specificoxidizing agent to form an aldehyde intermediate. The aldehydeintermediate is then reacted with a suitable reagent to form a chiralpolyketal comprise repeat structural units, wherein substantially allthe structural units comprise (i) at least one ketal group wherein atleast one ketal oxygen atom is within the polymer main chain; and (ii)at least one chiral group.

In certain embodiments, there s provided a method for preparing a chiralpolymer, said method comprising steps of: a) reacting an effectiveamount of an oxidizing agent with a polysaccharide to form a polyketalaldehyde; b) optionally treating the polyketal aldehyde with a suitablereagent under suitable conditions to form a polyketal; and c) optionallyrepeating step b) until the desired functionalization of said polyketalis achieved; thereby forming a chiral polymer, wherein said polymercomprises repeat structural units, wherein substantially all thestructural units comprise: i) at least one ketal group wherein at leastone ketal oxygen atom is within the polymer main chain; and ii) at leastone chiral group.

In certain embodiments, the method for preparing a chiral polymer,comprises steps of: a) reacting an effective amount of an oxidizingagent with a polysaccharide to form a polyketal aldehyde; b) optionallytreating the polyketal aldehyde with a suitable reagent to form apolyketal intermediate; c) optionally repeating step b) until thedesired functionalization of said polyketal intermediate is achieved;and d) reacting said polyketal intermediate with a suitable chiralreagent; thereby forming a chiral polymer, wherein said polymercomprises repeat structural units, wherein substantially all thestructural units comprise: i) at least one ketal group wherein at leastone ketal oxygen atom is within the polymer main chain; and ii) at leastone chiral group.

In a certain embodiment, at least a subset of the repeat structuralunits have the following structure:

wherein each occurrence of R¹ and R² is an organic moiety and includes acarbon atom or heteroatom covalently attached to C¹. R^(x) includes acarbon atom covalently attached to C². n is an integer. Each occurrenceof R³, R⁴, R⁵ and R⁶ is independently hydrogen or an organic moiety; andfor each occurrence of the bracketed structure n, at least one of C¹,C², R^(x), R¹, R², R³, R⁴, R⁵ and R⁶ is chiral.

In another embodiment of the invention, at least a subset of the repeatstructural units have the following structure:

wherein each occurrence of R² is an organic moiety and includes a carbonatom or heteroatom covalently attached to C¹; R^(x) includes a carbonatom covalently attached to C¹; n is an integer; each occurrence of R¹is an organic moiety; each occurrence of R³ and R⁴ is independentlyhydrogen or an organic moiety; and, for each occurrence of the bracketedstructure n, at least one of C¹, C², R^(x), R¹, R², R³ and R⁴ is chiral.

Each occurrence of R¹, R², R³, R⁴, R⁵ and R⁶ may be hydrophobic orhydrophilic, and may be the same or different throughout the polymer.Examples of organic moieties which are suitable include (but are notlimited to) branched and unbranched alkyl, alkenyl, alkynyl, haloalkyl,acyl, aryl, alkylaryl, heterocyclic group, heteroaryl, alkoxy,mercaptoalkyl, amino, alkylamino, dialkylamino, trialkylamino, cyano,hydroxy, halo, mercapto, nitro, carboxyaldehyde, carboxy,alkoxycarbonyl, carboxamide, carbamates, sulfonyl, sulfoxyl, andphosphate moieties.

In a preferred embodiment of the present invention, the chiralpolyketals comprise the structure:

In another preferred embodiment, the chiral polyketal of the inventioncomprise the structure:

wherein n is an integer.

In yet another embodiment, the chiral polyketals of the presentinvention can form linear or branched structures, and can havesubstitutents selected from the group consisting of branched andunbranched alkyl, alkenyl, alkynyl, haloalkyl, acyl, aryl, alkylaryl,heterocyclic group, heteroaryl, alkoxy, mercaptoalkyl, amino,alkylamino, dialkylamino, trialkylamino, cyano, hydroxy, halo, mercapto,nitro, carboxyaldehyde, carboxy, alkoxycarbonyl, carboxamide,carbamates, sulfonyl, sulfoxyl, and phosphate moieties.

Structure, yield and molecular weight of the resultant polyaldehydedepend on the initial polysaccharide. Polysaccharides that do notundergo significant depolymerization in the presence of glycol-specificoxidizing agents, for example, poly (2,1) and (2,6) fructoses, arepreferable. Examples of suitable polysaccharides include alpha and beta2,1 and 2,6 fructans. Particularly preferred polysaccharides are Inulin,Levans from plants, and bacterial fructans. Examples of suitableglycol-specific oxidizing agents include sodium periodate, leadtetra-acetate, periodic acid, etc. In certain embodiments, the oxidationsystem consists of a non-specific oxidizing agent in combination withglycol-specific catalyst or and intermediate oxidizer. Examples ofsuitable reducing agents include sodium borohydride, sodiumcyanoborohydride, etc. Temperature, pH and reaction duration can affectthe reaction rate and polymer hydrolysis rate. The reaction ispreferably conducted in the absence of light. One skilled in the art canoptimize the reaction conditions to obtain polymers of desiredcomposition. The resultant polymeric aldehyde intermediate may bereduced to the corresponding alcohol via a suitable reducing agent.Alternatively, aldehyde groups can be conjugated with a variety ofcompounds or converted to other types of functional groups. In anotherembodiment, the precursor carbohydrate has a chiral atom outside of thecleavage site. Thus the chirality of that atom is retained, and thepolyketal is chiral or optically active.

In certain embodiments, the polyketals of the present invention cancontain intermittent irregularities throughout the polyketal, such asincompletely oxidized saccharide moieties or additional groups in themain chain or in the side chains.

Since it is believed that oxidation does not affect configurations at C¹and C², the aldehyde intermediate and the polyketal retain theconfiguration of the parent polysaccharide and the polyketal is formedin stereoregular isotactic forms.

Fully Synthetic Route

In another preferred embodiment, the chiral polyketals of the presentinvention can be formed by combining a suitable initiator with a chiralprecursor compound comprising the chemical structure:

which forms a chiral polymer intermediate comprising the chemicalstructure:

wherein each occurrence of P¹ and P² includes a carbon atom covalentlyattached to C¹ and is independently an organic moiety or a protectedorganic moiety; P^(x) includes a carbon atom covalently attached to C²;n is an integer; each occurrence of P³, P⁴, P⁵ and P⁶ is independentlyhydrogen, an organic moiety or a protected organic moiety. For eachoccurrence of the bracketed structure n, at least one of C¹, C², P^(x),P¹, P², P³, P⁴, P⁵ and P⁶ is chiral. In a preferred embodiment, P¹, P²,P³, P⁴, P⁵ and P⁶ do not prevent polymerization. In one embodiment, whenappropriate, the protected organic moieties of the polymer intermediateare deprotected and optionally derivatized, thereby forming thepolyketal comprising the structure:

wherein each occurrence of R¹ and R² is an organic moiety and includes acarbon atom covalently attached to C¹; R^(x) includes a carbon atomcovalently attached to C²; n is an integer; each occurrence of R³, R⁴,R⁵ and R⁶ is independently hydrogen or an organic moiety; and, for eachoccurrence of the bracketed structure n, at least one of C¹, C², R^(x),R¹, R², R³, R⁴, R⁵ and R⁶ is chiral. Alternatively, other ring openingtechniques can be employed or developed, for example employingappropriate catalysts and resulting in the formation of polyketalscomprising unsaturated linkages within the main chain. The latter can befurther transformed into single bonds using appropriate reagents. Thus,in certain embodiments, a method for forming a chiral polymer comprisessteps of: a) reacting a suitable initiator with a compound having thechemical structure:

thereby forming a polymer intermediate comprising the chemicalstructure:

wherein each occurrence of P¹ and P² is independently an organic moietyor a protected organic moiety and includes a carbon atom covalentlyattached to C¹; each occurrence of P^(x) is independently an organicmoiety and includes a carbon atom covalently attached to C²; n is aninteger; each occurrence of P³, P⁴, P⁵ and P⁶ is independently hydrogen,an organic moiety or a protected organic moiety; and for each occurrenceof the bracketed structure n, at least one of C¹, C², P^(x), P¹, P², P³,P⁴, P⁵ and P⁶ is chiral; thereby forming a first polyketal intermediate;b) optionally reacting said first polymer intermediate with a suitablereagent to form a second polyketal intermediate; and c) optionallyrepeating step b) until the desired functionalization of said polyketalintermediate is achieved; thereby forming a polyketal comprising thestructure having the structure:

wherein each occurrence of R¹ and R² is independently an organic moietyand includes a carbon atom covalently attached to C¹; each occurrence ofR^(x) includes a carbon atom covalently attached to C²; n is an integer;each occurrence of R³, R⁴, R⁵ and R⁶ is independently hydrogen or anorganic moiety; and for each occurrence of the bracketed structure n, atleast one of C¹, C², R^(x), R¹, R², R³ and R⁴ is chiral.

In certain other embodiments, the method for forming a chiral polymercomprises steps of: a) reacting a suitable initiator with a compoundhaving the chemical structure:

thereby forming a polymer intermediate comprising the chemicalstructure:

wherein each occurrence of P¹ and P² is independently an organic moietyor a protected organic moiety and includes a carbon atom covalentlyattached to C¹; each occurrence of P^(x) is independently an organicmoiety and includes a carbon atom covalently attached to C²; n is aninteger; each occurrence of P³, P⁴, P⁵ and P⁶ is independently hydrogen,an organic moiety or a protected organic moiety; and for each occurrenceof the bracketed structure n, at least one of C¹, C², P^(x), P¹, P², P³,P⁴, P⁵ and P⁶ is chiral; thereby forming a first polyketal intermediate;b) optionally reacting said first polymer intermediate with a suitablereagent to form a second polyketal intermediate; and c) optionallyrepeating step b) until the desired functionalization of said polyketalintermediate is achieved; thereby forming a polyketal comprising thestructure having the structure:

wherein each occurrence of R¹ and R² is independently an organic moietyand includes a carbon atom covalently attached to C¹; each occurrence ofR^(x) includes a carbon atom covalently attached to C²; n is an integer;each occurrence of R³, R⁴, R⁵ and R⁶ is independently hydrogen or anorganic moiety; and for each occurrence of the bracketed structure n, atleast one of C¹, C², R^(x), R¹, R², R³ and R⁴ is chiral.

“Protected organic moiety,” as that term is used herein, means achemical group which will not interfere with decyclization of theprecursor compound by the initiator or prevent subsequentpolymerization, and which, upon additional treatment by a suitableagent, can be converted to an organic moiety. Examples of suitableorganic moieties include, but are not limited to, hydroxyl,hydroxyalkyl, amine, carboxyl, amide, carboxylic ester, thioester,aldehyde, nitryl, isonitryl, nitroso, hydroxylamine, mercaptoalkyl,heterocycle, carbamates, carboxylic acids and their salts, sulfonicacids and their salts, sulfonic acid esters, phosphoric acids and theirsalts, phosphate esters, polyglycol ethers, polyamines,polycarboxylates, polyesters, polythioesters, pharmaceutically usefulgroups, a biologically active substance or a diagnostic label.

Each occurrence of R¹, R², R³, R⁴, R⁵ and R⁶ may be hydrophobic orhydrophilic, and may be the same as or different than P¹, P², P³, P⁴, P⁵and P⁶, respectively.

In another embodiment of the invention, C¹, C², P^(x), P¹, P², P³, P⁴,P⁵ and P⁶ are not chiral, and the method of preparing the polyketalincludes a step whereby the polymer intermediate is reacted with asuitable chiral reagent to form a chiral polyketal (e.g., at least oneof R¹, R², R³, R⁴, R⁵ and R⁶ is chiral).

In another embodiment, the resultant chiral polyketal can be chemicallymodified by, for example, crosslinking the polyketals to form a gel. Thecrosslink density of the chiral polyketal is generally determined by thenumber of reactive groups in the polyketal and by the number ofcrosslinking molecules, and can be controlled by varying the ratio ofpolyketal to the amount of crosslinker present.

In one embodiment, a suitable crosslinking agent has the formulaX¹—(R)—X², where R is a spacer group and X¹ and X² are reactive groups.X¹ and X² may be the same or different. The spacer group R may be analiphatic, alicyclic, heteroaliphatic, heteroalicyclic, aryl orheteroaryl moiety. Examples of suitable spacer groups includebiodegradable or nonbiodegradable groups, for example, aliphatic groups,carbon chains containing biodegradable inserts such as disulfides,esters, etc. The term “reactive group,” as it relates to X¹ and X²,means functional groups which can be connected by a reaction within thepolyketals, thereby crosslinking the chiral polyketals. Suitablereactive groups which form crosslinked networks with the chiralpolyketals include epoxides, halides, tosylates, mesylates,carboxylates, aziridines, cyclopropanes, esters, N-oxysuccinimideesters, disulfides, anhydrides etc.

Alternatively, the term “reactive” group as it relates to X¹ and X²means a nucleophilic group that can be reacted with an aldehydeintermediate of the chiral polyketals, thereby crosslinking said chiralpolyketals. Suitable reactive groups for the aldehyde intermediateinclude amines, thiols, polyols, alcohols, ketones, aldehydes,diazocompounds, boron derivatives, ylides, isonitriles, hydrazines andtheir derivatives and hydroxylamines and their derivatives, etc.

In yet another embodiment, the chiral polyketals of this invention canhave a variety of functional groups. For example, aldehyde groups of anintermediate product of polysaccharide oxidation can be converted notonly into alcohol groups, but also into amines, thioacetals, carboxylicacids, amides, esters, thioesters, etc.

In certain embodiments, terminal groups of the polymers of thisinvention can differ from R¹, R², R³, R⁴, R⁵ or R⁶. Terminal groups canbe created, for example, by selective modification of each reducing andnon-reducing terminal unit of the precursor polysaccharide. One skilledin the art can utilize known chemical reactions to obtain desiredproducts with varying terminal groups. For example, a hemiketal group atthe reducing end of a polyketose can be readily and selectivelytransformed into a carboxylic acid group (e.g., via formation of acarboxyl-substituted glycoside) and further into a variety of otherfunctional groups.

In one embodiment, the terminal group is such that it allows binding ofthe polymeric chain to a solid support either directly or via a suitablelinker. This has the advantage of allowing solid phase chemicalmodification of the immobilized polymer to the desired chiral polyketalof the invention. Benefits of this technique include ease ofpurification by filtration, use of excess reagent for driving reactionsto completion, and ease of automation. Examples of suitable solidsupport are polystyrene, polyethylene glycol, cellulose, controlledpore-glass, etc. . . . . Examples of suitable linkers are those that canbe cleaved under neutral or basic conditions, such as ester or sulfidelinkages.

In another embodiment of the invention, the chiral polyketal isassociated with a macromolecule for applications in affinitychromatography. Examples of macromolecules include, but are not limitedto, receptors, enzymes, proteins and antibodies.

In certain embodiments, there is provided a composition comprising achiral polyketal; wherein said chiral polyketal is the macromolecularproduct of the lateral cleavage of a polysaccharide; whereby at leastone carbon-carbon bond is cleaved in substantially all the carbohydratemoieties of said polysaccharide. In certain other embodiments, thecleavage is effected using an oxidizing agent. In yet other embodiments,the oxidizing agent is a glycol-specific agent. In still otherembodiments, the glycol-specific agent is sodium periodate. In a furtherembodiment, the oxidizing agent is non-specific and is used incombination with a glycol-specific catalyst.

In certain embodiments, the compositions provided herein comprise achiral polyketal; wherein said chiral polyketal is the macromolecularproduct of the lateral cleavage of a polysaccharide; whereby at leastone carbon-carbon bond is cleaved in substantially all the carbohydratemoieties of said polysaccharide; wherein said macromolecular product isobtained by any one of the methods described herein.

Chiral Polyketals—Applications to Chromatographic Methods

In another aspect of the present invention, chiral polyketals inaccordance with the invention may be used in liquid chromatography, forexample as part of the mobile phase in a reversed-phase system employinga C-18 column. Especially in chromatographic systems, chiral polymers inaccordance with the present invention may be used on a preparative scaleto purify large quantities of racemic mixtures.

In chromatographic applications, chiral polyketals in accordance withthe present invention may be present in the mobile phase, or they couldinstead be incorporated into chiral stationary phases such as gels, wallcoatings, and packed columns and capillaries through means known in theart. For example, a gas chromatography capillary column may be packedwith silica particles that have been coated with the chiral polymer.Another possibility is the combination of a chiral mobile phaseincorporating the chiral polymer in accordance with the presentinvention, with a different chiral stationary phase. This combinationcan result in separation efficiencies that are greater than the sum ofthe parts.

The invention further encompasses the use of the chiral stationaryphases according to the invention for the separation of optical isomers,in particular of racemic mixtures into the optical antipodes. Thecomposition of the mobile phase can be chosen and optimized in thecustomary manner, according to the nature and property of the racemateto be separated. Where a particular set of conditions results in theseparation of two enantiomers, then the same or similar conditionsshould, in general, also successfully separate homologues of thoseenantiomers, as well as other enantiomers with similar structures. Thusthe chiral polyketals of the invention may find use in chromatographicmethod development. In certain embodiments, the chiral polyketals of theinvention are utilized for the separation of optical isomers.

When the polyketal is associated with a macromolecule (for example,receptors, enzymes, proteins, antibodies and the like), the inventionencompasses applications in affinity chromatography (e.g.,chromatographic techniques that revolve around compound-dependent“specific binding” as a way to differentiate two or more compounds in atest solution). Specific binding is, for example, the affinity exhibitedbetween a receptor molecule and a compound wherein the receptor moleculeincludes a defined binding locus that discriminatorily binds thosecompounds which have a predetermined chemical structure. Compounds nothaving the predetermined chemical structure do not bind with the bindingsite of the receptor molecule.

Chiral Polyketals—Source for Chiral Compounds

In one embodiment, the chiral polyketals of the present inventionconstitute an alternative source for chiral compounds.

Due to the wide variety of the substitutents (R¹-R⁶) that can be used,the chemical properties of the polyketals described in the presentinvention can be modified with great versatility, and thus can beoptimized for a particular application. In particular, they can allowaccess to a wide variety of chiral compounds useful for asymmetricsynthesis.

In one embodiment, depolymerization (e.g., hydrolysis, acidolysis orenzymatic degradation) of the polyketals of the present invention willresult in the monomeric components ketones and alcohols, or inhydroxyketones. The ketones and hydroxyketones may further isomerize,e.g., to the corresponding hydroxyaldehydes, depending on theirstructure. These monomeric components can be used as chiral startingmaterial for various enantiomeric syntheses. Furthermore, said monomericcomponents can be “custom-designed” by suitable chemical modificationsof the parent polyketal. In a preferred embodiment, ketone derivativesare generated without isomerization via depolymerization of protectedhydrophilic polyketals in non-aqueous media.

Thus the invention encompasses chiral compounds, wherein said compoundsare the depolymerization product of the chiral polyketal of theinvention. In certain embodiments, the inventive chiral compounds arederived from the depolymerization of a chiral polyketal of theinvention; wherein said chiral polyketal is prepared by any one of themethods described herein.

Throughput this document, various publications are referred to, each ofwhich is hereby incorporated by reference in its entirety in an effortto more fully describe the state of the art to which the inventionpertains.

The invention will now be further and specifically described by thefollowing examples. All parts and percentages are by weight unlessotherwise stated.

EQUIVALENTS

The representative examples that follow are intended to help illustratethe invention, and are not intended to, nor should they be construed to,limit the scope of the invention. Indeed, various modifications of theinvention and many further embodiments thereof, in addition to thoseshown and described herein, will become apparent to those skilled in theart from the full contents of this document, including the exampleswhich follow and the references to the scientific and patent literaturecited herein. It should further be appreciated that the contents ofthose cited references are incorporated herein by reference to helpillustrate the state of the art.

The following examples contain important additional information,exemplification and guidance that can be adapted to the practice of thisinvention in its various embodiments and the equivalents thereof.

EXEMPLIFICATION

The practitioner has a well-established literature of polymer chemistryto draw upon, in combination with the information contained herein, forguidance on synthetic strategies, protecting groups, and other materialsand methods useful for the synthesis of the polyketals of thisinvention.

The various references cited herein provide helpful backgroundinformation on preparing polymers similar to the inventive compoundsdescribed herein or relevant intermediates, as well as information onformulation, uses, and administration of the polyketals of theinvention, which may be of interest.

Moreover, the practitioner is directed to the specific guidance andexamples provided in this document relating to various exemplarypolyketals and intermediates thereof.

The polyketals of this invention and their preparation can be understoodfurther by the examples that illustrate some of the processes by whichthese compounds are prepared or used. It will be appreciated, however,that these examples do not limit the invention. Variations of theinvention, now known or further developed, are considered to fall withinthe scope of the present invention as described herein and ashereinafter claimed.

According to the present invention, any available techniques can be usedto make or prepare the inventive polyketals or compositions includingthem. For example, a variety of solution phase synthetic methods such asthose discussed in detail below may be used. Alternatively oradditionally, the inventive polyketals may be prepared using any of avariety combinatorial techniques, parallel synthesis and/or solid phasesynthetic methods known in the art.

It will be appreciated as described below, that a variety of inventivepolyketal can be synthesized according to the methods described herein.The starting materials and reagents used in preparing these compoundsare either available from commercial suppliers such as Aldrich ChemicalCompany (Milwaukee, Wis.), Bachem (Torrance, Calif.), Sigma (St. Louis,Mo.), or are prepared by methods well known to a person of ordinaryskill in the art following procedures described in such references asFieser and Fieser 1991, “Reagents for Organic Synthesis”, vols 1-17,John Wiley and Sons, New York, N.Y., 1991; Rodd 1989 “Chemistry ofCarbon Compounds”, vols. 1-5 and supps, Elsevier Science Publishers,1989; “Organic Reactions”, vols 1-40, John Wiley and Sons, New York,N.Y., 1991; March 2001, “Advanced Organic Chemistry”, 5th ed. John Wileyand Sons, New York, N.Y.; Larock 1990, “Comprehensive OrganicTransformations: A Guide to Functional Group Preparations”, 2^(nd) ed.VCH Publishers; and other references more specifically drawn to polymerchemistry. The methods described below are merely illustrative of somemethods by which the polyketals of this invention can be synthesized,and various modifications to these methods can be made and will besuggested to a person of ordinary skill in the art having regard to thisdisclosure.

The starting materials, intermediates, and polyketals of this inventionmay be isolated and purified using conventional techniques, includingfiltration, distillation, crystallization, chromatography, and the like.They may be characterized using conventional methods, including physicalconstants and spectral data.

Example 1 Formation of Polyaldehydketal by Inulin Oxidation

Inulin from Chicory (polymerization degree ca. 35), 0.5 g was dissolvedin 10 mL water at 60° C. The solution was cooled to room temperature andmixed with a suspension of 0.8 g sodium periodate in 2 mL of water.After overnight incubation, the reaction mixture was filtered andstudied by size exclusion HPLC. It was found that periodate oxidationresults in a small shift of the molecular weight distribution towardslower molecular weights.

Example 2 Formation of Polyalcohol Polyketal by PolyaldehydroketalReduction

The reaction mixture of Example 1 was cooled to 0° C. (ice-bath), andwas slowly poured into a cold solution of 1 g sodium borohydride in 2 mlwater under stirring. The reaction mixture was kept on ice bath toprevent the temperature from rising above 20° C.

The reaction mixture was studied by size exclusion HPLC. Borohydridereduction was not found to further affect the apparent molecular weightdistribution (FIG. 1). The product was further isolated by gelchromatography on Sephadex G-25 and lyophilized. The purified productwas then studied by proton NMR spectroscopy. The obtained spectrum (FIG.2) fully corresponded to the expected structure of poly[1-hydroxymethyl-1-(2-hydroxy-1-hydroxymethyl-ethoxy)-ethylene oxide],or PHMHO:

Example 3 Oxidation of Levan

Levan (purchased from Sigma-Aldrich), 0.5 g was suspended in 10 mL waterat 90° C. The solution was cooled to room temperature and mixed with asuspension of 0.9 g sodium periodate in 2 mL of water. After overnightincubation on a shaker, the reaction mixture was filtered and studied bysize exclusion HPLC. It was found that periodate oxidation results inshift of the molecular weight distribution towards approximately twicelower molecular weights than of original Levan.

Example 4 Reduction of Levan

The reaction mixture of Example 3 was cooled to 0° C. (ice-bath), andwas slowly poured into a cold solution of 1 g sodium borohydride in 2 mlwater under stirring. The reaction mixture was kept on ice bath toprevent the temperature from rising above 20° C.

The reaction mixture was studied by size exclusion HPLC. Borohydridereduction was found to have no effect on the apparent molecular weightdistribution (FIG. 3). The product was further isolated by gelchromatography on Sephadex G-25 and lyophilized. The purified productwas studied by proton NMR spectroscopy. The obtained spectrum (FIG. 4)fully corresponded to the expected structure ofpoly(hydroxymethylethylene di(hydroxymethyl)ketal), or PHMK:

Example 5 Modification of Polyketal with Succinic Anhydride

PHMK (Example 4), 10 mg, and succinic anhydride, 2 mg, and pyridine, 5μl, were dissolved in 100 μl DMSO. After overnight incubation, thereaction mixture was diluted with water to 1 ml and desalted by gelfiltration on Sephadex G-25. The resultant polymer, succinyl-PHMK, waslyophilized.

Example 6 Modification of Succinylated Polyketal with Trypsin

Succinyl-PHMK (Example 5), 2 mg, and trypsin, 1 mg, were dissolved in 50μl H₂O, N-Ethyl-N′-diethylaminopropylcarbodiimide (EDC), 2 mg, wasdissolved in 50 μl of 50 mM phosphate buffer solution, pH=6.5, and addedto the solution of Succinyl-PHMK and trypsin. After a 60 min incubation,the resultant conjugate of Succinyl-PHMK and trypsin was separated fromthe unbound trypsin by size exclusion HPLC equipped with refractionindex and UV (260 nm) detectors.

Example 7 Modification of Oxidized Inulin with Doxorubicin

Oxidized inulin (polyaldehydroketal of Example 1) was prepared asdescribed above and desalted by gel chromatography on Sephadex G-25. 1ml of a 40 mg/ml solution of the polyaldehydroketal were mixed with 1 mlof 5 mg/ml solution of doxorubicin. Sodium cyanoborohydride (50 mg) wasadded to the solution, and the pH of the reaction mixture was adjustedto 7 with 1 M NaOH. After a 180 min incubation, the conjugate wasseparated from the unbound doxorubicine by gel filtration andlyophilized. Doxorubicine content was determined photometrically and wasfound to be 0.11 mg/mg of dry substance.

Example 8 Cross-Linking of Levan Polymer

PHMK (Example 4), 100 mg, and NaOH, 20 mg, were dissolved in 200 μl H₂O.Epichlorohydrin, 20 μl, was added under stirring. The mixture wasincubated on a shaker for 5 hours. Then, the reaction mixture was heatedin a boiling water bath for 1 hour. The resultant gel was extracted fromthe reactor, washed with water, and dried in absolute ethanol.

Example 9 Inulin-Lipid Conjugate Random Point Modification

Oxidized inulin was prepared as described in example 1, except thatperiodate concentration was reduced 5-fold. Oxidized inulin was desaltedby gel chromatography on Sephadex G-25. 1 ml of a 40 mg/ml solution ofthe oxidized inulin containing 10 mg of sodium cyanoborohydride wasmixed with 0.25 ml of 10 mg/ml solution ofdistearoylphosphatidylethanolamine (DSPE) in methanol. The pH of thereaction mixture was adjusted to 8 with 1 M NaOH. After a 48 hrincubation on a shaker, the reaction mixture was filtered through a 0.22μm membrane filter, and the product was purified by gel chromatographyon Sephadex G-25. and lyophilized. After lyophilization, the product waswashed with chlorophorm and dried in vacuum. The effective size ofmicelles formed by the product in water, as determined by SEC HPLC, wasmore than 15 nm.

Example 10 Transformation of Inulin-Lipid Conjugate into Polyketal-LipidConjugate

Inulin-DSPE conjugate of Example 8, 10 mg, was suspended in water, 100μl. Then, 20 mg of sodium periodate were added under stirring, and thereaction mixture was incubated for 5 hours. After the incubation, thesolution was mixed with 1 ml of 10% solution of sodium borohydride.After 60 min. incubation, the reaction mixture was neutralized with HCl,ant the product was purified by gel chromatography and lyophilized.

Example 11 Polyketal Conjugation with DTPA

PHMK (Example 4), 10 mg, and dicycloanhydride ofdiethylenetriaminepentaacetic acid (DTPA-CA), 1 mg, were dissolved in100 μl DMF. 0.1 mg of tosylsulfonic acid were added as catalyst. Afteran overnight incubation, the reaction mixture was diluted with water to1 ml and desalted by gel filtration on Sephadex G-25. The resultantpolymer, DTPA-PHMK, was lyophilized.

Example 12 Polyketal-DTPA Conjugate Labeling with In-111

1 mg of DTPA-PHMK of Example 10 were dissolved in 100 μl water and mixedwith solution of [¹¹¹In]Cl, 156 μCi, in 50 μl 0.5 N sodium citratebuffer, pH=5.6. After 30 min. incubation, the radiolabeled polymer wasseparated by gel chromatography on Sephadex G-25 and analyzed by sizeexclusion HPLC. The radiochemical purity was found to be >98%; activityof polymer-bound Indium-111: 97 μCi.

Example 13 Administration of Labeled Polyketal into Rat and ModelDiagnostic Procedure

The radiolabeled DTPA-PHMK of Example 11, 37 μCi, was injected throughthe tail vein into a 360 g normal male Sprague-Dawley CD ratanesthetised with sodium pentobarbital and positioned on gamma camerafor dynamic image acquisition. Image acquisition protocol (16 images, 60sec. each) was activated simultaneously with polymer injection. Theprocess of biodistribution of the radiolabeled polyketal was observed onthe screen of the gamma camera and recorded (16 images, 60 sec. each).Images showed that, during the first 16 min. after injection, thepolymer was circulating in blood with slow renal filtration.

Example 14 Acute Toxicity of PHMHO

PHMHO was dissolved in 0.9% NaCl (100 mg/ml) and injected intravenouslyinto 6 mice at 100 mg/kg body weight. Animals were observed for 30 daysafter the injection. All animals survived; none showed any detectablesigns of toxicity.

1-35. (canceled)
 36. A method comprising steps of: a) reacting aneffective amount of an oxidizing agent with a polysaccharide to form abiodegradable biocompatible acyclic polyketal aldehyde; b) optionallytreating the biodegradable biocompatible acyclic polyketal aldehyde witha suitable reagent under suitable conditions to form a biodegradablebiocompatible acyclic polyketal; and c) optionally repeating step b)until the desired functionalization of the biodegradable biocompatibleacyclic polyketal is achieved; thereby forming a biodegradablebiocompatible acyclic polyketal comprising repeat structural units,wherein substantially all the structural units comprise: i) at least oneketal group wherein at least one ketal oxygen atom is within the polymermain chain, wherein the ketal group is acyclic; and ii) at least onehydrophilic group or pharmaceutically useful group.
 37. The method ofclaim 36, further comprising the step of reacting the biodegradablebiocompatible acyclic polyketal with a crosslinking agent.
 38. Themethod of claim 36, further comprising the step of reacting thebiodegradable biocompatible acyclic polyketal aldehyde intermediate witha crosslinking agent.
 39. A method of administering to a patient in needof treatment, comprising administering to the subject an effectiveamount of a suitable therapeutic agent associated with a biodegradablebiocompatible polyketal; wherein the biodegradable biocompatiblepolyketal is an acyclic polyketal comprising repeat structural units,wherein substantially all the structural units comprise: a) at least oneketal group wherein at least one ketal oxygen atom is within the polymermain chain, wherein the ketal group is acyclic; and b) at least onehydrophilic group or pharmaceutically useful group.
 40. The method ofclaim 39, wherein the biodegradable biocompatible polyketal is a polymermatrix and the suitable therapeutic agent is associated with andreleased from the biodegradable biocompatible polyketal matrix bydegradation of the polymer matrix or diffusion of the agent out of thepolymer matrix over a period of time.
 41. The method of claim 40,wherein the step of administering the therapeutic agent comprisesdelivery by implantation of the biodegradable biocompatible polyketalmatrix incorporating the therapeutic agent.
 42. The method of claim 39,wherein the biodegradable biocompatible polyketal comprises structuralunits having the structure:

wherein each occurrence of R¹ and R² is independently a biocompatiblegroup and includes a carbon atom covalently attached to C¹; eachoccurrence of R^(x) is a carbon atom covalently attached to C²; n is aninteger; each occurrence of R³, R⁴, R⁵ and R⁶ is a biocompatible groupand is independently hydrogen or an organic moiety; and for eachoccurrence of the bracketed structure n, at least one of R¹, R², R³, R⁴,R⁵ and R⁶ is a hydrophilic group or a pharmaceutically useful group. 43.The method of claim 39, wherein the biodegradable biocompatiblepolyketal comprises structural units having the structure:

wherein each occurrence of R¹ is a biocompatible group; each occurrenceof R² is a biocompatible group and includes a carbon atom covalentlyattached to C¹; each occurrence of R^(x) is a carbon atom covalentlyattached to —C¹—O—; n is an integer; each occurrence of R¹, R³ and R⁴ isa biocompatible group and is independently hydrogen or an organicmoiety; and for each occurrence of the bracketed structure n, at leastone of R¹, R², R³, and R⁴ is a hydrophilic group or a pharmaceuticallyuseful group.
 44. The method of claim 39, wherein the step ofadministering the therapeutic agent comprises a therapeutic agentselected from the group consisting of: vitamins, anti-AIDS substances,anti-cancer substances, antibiotics, immunosuppressants, anti-viralsubstances, enzyme inhibitors, neurotoxins, opioids, hypnotics,anti-histamines, lubricants, tranquilizers, anti-convulsants, musclerelaxants and anti-Parkinson substances, anti-spasmodics and musclecontractants including channel blockers, miotics and anti-cholinergics,anti-glaucoma compounds, anti-parasite and/or anti-protozoal compounds,modulators of cell-extracellular matrix interactions including cellgrowth inhibitors and anti-adhesion molecules, vasodilating agents,inhibitors of DNA, RNA or protein synthesis, anti-hypertensives,analgesics, anti-pyretics, steroidal and non-steroidal anti-inflammatoryagents, anti-angiogenic factors, anti-secretory factors, anticoagulantsand/or antithrombotic agents, local anesthetics, ophthalmics,prostaglandins, anti-depressants, anti-psychotic substances,anti-emetics, imaging agents.
 45. The method of claim 39, wherein thestep of administering the therapeutic agent further comprisesadministering additional biologically active compounds selected from thegroup consisting of vitamins, anti-AIDS substances, anti-cancersubstances, antibiotics, immunosuppressants, anti-viral substances,enzyme inhibitors, neurotoxins, opioids, hypnotics, anti-histamines,lubricants, tranquilizers, anti-convulsants, muscle relaxants andanti-Parkinson substances, anti-spasmodics and muscle contractantsincluding channel blockers, miotics and anti-cholinergics, anti-glaucomacompounds, anti-parasite and/or anti-protozoal compounds, modulators ofcell-extracellular matrix interactions including cell growth inhibitorsand anti-adhesion molecules, vasodilating agents, inhibitors of DNA, RNAor protein synthesis, anti-hypertensives, analgesics, anti-pyretics,steroidal and non-steroidal anti-inflammatory agents, anti-angiogenicfactors, anti-secretory factors, anticoagulants and/or antithromboticagents, local anesthetics, ophthalmics, prostaglandins,anti-depressants, anti-psychotic substances, anti-emetics, imagingagents, and combination thereof.
 46. The method of claim 39, wherein thebiodegradable biocompatible polyketal is further associated with adiagnostic label.
 47. The method of claim 46, wherein the diagnosticlabel is selected from the group consisting of: fluorophores,radiopharmaceutical or radioactive isotopes for gamma scintigraphy andPET, contrast agents for Magnetic Resonance Imaging (MRI), contrastagents for computed tomography, contrast agents for X-ray imagingmethod, agents for ultrasound diagnostic method, agents for neutronactivation, moieties which can reflect, scatter or affect X-rays,ultrasounds, radiowaves and microwaves.
 48. The method of claim 46,wherein the biodegradable biocompatible polyketal is further monitoredin vivo.
 49. A biodegradable biocompatible acyclic polyketal comprisingrepeat structural units, wherein substantially all the structural unitscomprise: a) at least one ketal group wherein at least one ketal oxygenatom is within the polymer main chain, wherein the ketal group isacyclic; and b) at least one hydrophilic group or pharmaceuticallyuseful group, wherein the biodegradable biocompatible acyclic polyketalis associated with a macromolecule.
 50. The biodegradable biocompatibleacyclic polyketal of claim 49, wherein at least a subset of thestructural units have the structure:

wherein each occurrence of R¹ and R² is independently a biocompatiblegroup and includes a carbon atom covalently attached to C¹; eachoccurrence of R^(x) is a carbon atom covalently attached to C²; n is aninteger; each occurrence of R³, R⁴, R⁵ and R⁶ is a biocompatible groupand is independently hydrogen or an organic moiety; and for eachoccurrence of the bracketed structure n, at least one of R¹, R², R³, R⁴,R⁵ and R⁶ is a hydrophilic group or a pharmaceutically useful group. 51.The biodegradable biocompatible acyclic polyketal of claim 49, whereinat least a subset of the structural units have the structure:

wherein each occurrence of R¹ is a biocompatible group; each occurrenceof R² is a biocompatible group and includes a carbon atom covalentlyattached to C¹; each occurrence of R^(x) is a carbon atom covalentlyattached to —C¹—O—; n is an integer; each occurrence of R¹, R³ and R⁴ isa biocompatible group and is independently hydrogen or an organicmoiety; and for each occurrence of the bracketed structure n, at leastone of R¹, R², R³, and R⁴ is a hydrophilic group or a pharmaceuticallyuseful group.
 52. The biodegradable biocompatible acyclic polyketal ofclaim 49, wherein the macromolecule is a nucleic acid.
 53. Thebiodegradable biocompatible acyclic polyketal of claim 52, wherein themacromolecule is DNA.
 54. The biodegradable biocompatible acyclicpolyketal of claim 52, wherein the macromolecule is RNA.
 55. Thebiodegradable biocompatible acyclic polyketal of claim 49, wherein themacromolecule is a protein or peptide.
 56. The biodegradablebiocompatible acyclic polyketal of claim 55, wherein the macromoleculeis an enzyme.
 57. The biodegradable biocompatible acyclic polyketal ofclaim 52, wherein the association between the biodegradablebiocompatible polyketal and nucleic acid is covalent.
 58. Thebiodegradable biocompatible acyclic polyketal of claim 52, wherein theassociation between the biodegradable biocompatible polyketal andnucleic acid is non-covalent.
 59. The biodegradable biocompatibleacyclic polyketal of claim 58, wherein the association between thebiodegradable biocompatible polyketal and nucleic acid is selected fromhydrogen bonding, van der Waals interactions, hydrophobic interactions,magnetic interactions, electrostatic interactions, or a combinationthereof.
 60. The biodegradable biocompatible acyclic polyketal of claim59, wherein the association between the biodegradable biocompatiblepolyketal and nucleic acid is electrostatic.